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Title: The Geologic Story of Glacier National Park
Author: Dyson, James L.
Language: English
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The Geologic Story
of
Glacier National Park
{Cover} CHIEF MOUNTAIN
Special Bulletin No. 3
GLACIER NATURAL HISTORY ASSOCIATION
Price 25 Cents
THE GEOLOGIC STORY
of
GLACIER NATIONAL PARK
By JAMES L. DYSON
Head, Department of Geology and Geography
Lafayette College[1]
Until recently a geologist was visualized by most people as a queer sort
of fellow who went around the countryside breaking rocks with a little
hammer. Fortunately, the general public today has a much clearer picture
of the geologist and his science, but there are still many among us who
mistakenly feel that geology is something too remote for practical
application.
Geology is the science of the Earth. It includes a history of our planet
starting with its origin, and a history of the life which has lived upon
it. From it we can determine the reason for every feature of the
landscape and every rock structure underneath the surface, and we can
further learn what processes gave rise to them.
Practically everything to be seen on the face of the Earth owes its
origin directly or indirectly to geological processes. These may be
grouped into two great categories: Internal forces or agents which
raise, lower, bend, and break the Earth’s crust; and external, more
familiar agents such as water, wind, and ice, which wear away the
surface and carry the materials to another place—ultimately to the sea.
Let us consider a few of the products of these geologic agents: (1) The
soil covering most of the landscape and furnishing the plant products
which serve as our food; (2) the solid rock, so conspicuous in all
mountain ranges; (3) the hills, the valleys, and the mountains; (4) all
the streams, ponds, lakes—even the sea. If you live in a place where man
has covered up the rock and the soil evidence of geological processes is
yielded by the buildings themselves, whether they be of stone quarried
from the Earth’s crust, or of brick made from clay. The stone and brick
are supported by a framework of steel originally taken from a mine in
the form of iron ore. The concrete and asphalt of the roads came from
rocks within the Earth, as did every drop of gasoline which plays so
vital a part in world affairs today. Even those commonplaces of American
life, the bottle and the “tin” can, are products of geology. As you read
this you need look only at your watch or perhaps an item of jewelry
which you wear to see something—gold, silver, platinum, a diamond or
other gem stone—which is a part of geology.
Thus, from here it is a short step to the realization that a number of
geologic processes and agents working over long periods of time have
given rise to innumerable features and structures ranging from the
loftiest mountains down to the smallest hills and valleys; from the soil
which grows our food to the gasoline and coal which feed our industries;
from our huge iron ore deposits down to the much smaller, but now no
less significant, deposits of uranium.
How is all this related to a national park? Nowhere within our land can
the accomplishments of the great geological processes, or their
present-day operation, be seen to better advantage than in many of our
national parks and monuments. In fact, it is for this reason principally
that many of them were established. Notable is Grand Canyon National
Park, containing the most spectacular part of the Colorado’s mile-deep
canyon cut during the past million or so years through a series of rocks
which themselves record a billion or more years of Earth history. Mount
Rainier is the largest volcano in the United States. On it glaciers are
now wearing away materials formerly extruded and piled up to spectacular
height by volcanic forces. Crater Lake lies in the sunken throat of a
volcano which at one time probably rivaled Rainier in size. In Carlsbad
Caverns and Mammoth Cave National Parks are two of the world’s largest
caverns which clearly demonstrate the tremendous effectiveness of
subsurface water in dissolving limestone. Bryce Canyon and Zion National
Parks and the Badlands National Monument illustrated on a much smaller
but no less spectacular scale than the Grand Canyon the wonderful
erosive power of running water. In Grand Teton one can see a huge block
of the crust which has been raised thousands of feet along a high-angle
fault, and at Lassen Peak in California and Craters of the Moon in Idaho
there are exhibited some of the most recent volcanic features north of
the Rio Grande. Despite Yellowstone’s wildlife and fishing it is best
known perhaps for its geysers. This brief list is by no means complete,
for something of prime geologic interest can be found in almost every
national park and monument.
Now we come to Glacier National Park. Within its boundaries there
perhaps is exhibited a greater variety of geologic features than in any
of the others. Much of the park lies above timberline so that the rocks
which comprise its mountains are exposed to view. Held within these
superb mountains is an entertaining geologic story which they are
anxious and willing to tell us. All we need to do is unlock the door
with the key the geologist gives us and then go see for ourselves. Why
do the mountains rise so precipitously above the plains? What is that
conspicuous black band across the faces of so many of the peaks, and how
did it get there? Why are some of the rocks so red? The answers to these
and other questions come out as the geologic story unfolds. The American
people are interested in this story for they realize that to understand
what they see is to increase their enjoyment thousandfold.
Chart of Geologic Time
(FOR A CHRONOLOGICAL ORDER OF EVENTS, THE CHART SHOULD BE READ FROM
BOTTOM TO TOP)
ERAS PERIODS DATES EVENTS IN GLACIER PARK AREA
CENOZOIC
The Present
Post Glacial Erosion of the mountains; formation of
alluvial fans and talus cones.
15,000 B.C.
Pleistocene Birth of modern glaciers.
Appearance of present forests.
1,000,000 B.C.
Pliocene Extensive glaciation. Formation of lakes,
waterfalls, horn peaks, cirques. Valleys
scoured deeply by glaciers.
Miocene Disappearance of forests.
Oligocene Mountains worn down, raised, eroded again.
Eocene Lewis overthrust probably occurred early
in Eocene.
58,000,000 B.C.
MESOZOIC Great mountain building (Rocky Mountain
revolution) by forces which eventually
formed Lewis overthrust. Sea withdrew and
never again returned. Thick accumulation
of marine sediments. Invertebrates
abundant in sea. Expansion of the sea.
Cretaceous
127,000,000 B.C.
Jurassic
Triassic Dinosaurs probably inhabited park and
nearby area.
182,000,000 B.C.
PALEOZOIC Seas covered region during much of era.
Permian
Carboniferous
255,000,000 B.C.
Devonian
Silurian
Ordovician
Cambrian
510,000,000 B.C.
PROTEROZOIC Sea withdrew and region was eroded at end
of era.
Area covered by sea in which Belt
sediments were deposited.
Algae lived in sea. Intrusions (diorite
sill and dikes) from flows (Purcell) of
igneous material.
ARCHEOZOIC 2,110,000,000 B.C. ?
ERAS, PERIODS, AND DATES IN THIS CHART ARE IN ACCORDANCE WITH THOSE
WHICH HAVE BEEN ADOPTED AS OFFICIAL BY THE NATIONAL PARK SERVICE.
The Story Begins
The most striking feature of the mountains—certainly the one which comes
first to a visitor’s attention—is the color banding. No matter where one
looks this feature greets his view. If he enters the park at the St.
Mary Entrance, there ahead on the sides of Singleshot and East Flattop
Mountains are white and purple bands. Should he enter first the
Swiftcurrent Valley, he would soon note the banding in the mountains
lying to his right and left, and finally culminating in the precipitous
Garden Wall at the head of the valley. The visitor soon realizes that
every mountain within the park is composed of rock layers of various
colors. With very few exceptions these strata are of sedimentary origin;
that is, they accumulated by depositions of muds and sands in a body of
water and are now mainly limestones, shales, and sandstones. These
sedimentary rocks all belong to a single large unit known as the Belt
series, so named because of exposures in the Little Belt and Big Belt
Mountains farther south in Montana. In Glacier National Park these
rocks, which have a maximum thickness of more than 20,000 feet, are in
the form of a large syncline (downfold), the east and west edges of
which form the crests of the Lewis and Livingstone Ranges (Figure 3D).
Throughout the large area of western Montana, northern Idaho, and
southern British Columbia where Belt rocks occur, they are important
mountain-makers. In addition to the ranges already mentioned they are
the principal rocks in many others, including the Mission, Swan, and
Flathead in the region south of Glacier Park; the Bitterroot and Coeur
d’Alene between Idaho and Montana; and the Purcell in British Columbia.
Further, rocks of similar age form the core of the Uinta Range in Utah
and the lower section of the Grand Canyon in Arizona.
During the Proterozoic Era of Earth history a long, narrow section of
North America extending from the Arctic Ocean southward, probably as far
as Arizona and southern California, slowly sank to form a large,
shallow, sea-filled trough known as a geosyncline (Figure 1). Streams
from adjacent lands carried muds and sands into the sea, at times almost
completely filling it. Inasmuch as thousands of feet of sediments were
deposited, the geosyncline must have continued to sink throughout the
period of sedimentation. Eventually the muds were compacted into shales,
or limestones if they contained a lot of lime, and the sands into
sandstones. These are the rocks we now know as the Belt series. The
surfaces of many of the sandstone layers are covered with ripple marks
which could have been made only by wave and current action in shallow
water. Mudcracks on many of the shale beds prove that at times the
sediments, probably near the mouths of rivers were exposed to the air
long enough to dry out. Great thicknesses of limestone and numerous
fossils of calcareous algae, primitive marine plants, are evidences that
the body of water was a sea.
FIGURE 1. BELT GEOSYNCLINE
Throughout the geologic past the appearance and disappearance of seas on
the continents have been frequent events. In fact such changes are
slowly taking place even today. Hudson Bay and the Baltic and North Seas
are examples of shallow seas situated on the continents. The area around
Hudson Bay is rising; as attested by the fact that some of the fish
weirs constructed in water along the shore during the past several
hundred years are now a considerable distance inland. We know also that
our Atlantic coast has been subsiding for a number of years at an annual
rate of about 0.02 feet. To be sure, these movements are slow, but if
continued over a long period they might conceivably make some rather
profound changes, even as the birth and death of the Belt sea.
Within Glacier National Park the Belt series is divided on the basis of
lithologic differences into six distinct formations. Because each has a
characteristic color, these formations can easily be identified, often
from distances of several miles. Usually two, sometimes three or four,
of them comprise a single mountain, the oldest always at the mountain
base and the youngest on the summit, this being the relative position in
which they were deposited in the form of sediment.
[Illustration: MUD CRACKS ON A LAYER OF THE APPEKUNNY FORMATION
(PHOTO BY C. L. FENTON. OUR AMAZING EARTH. DOUBLEDAY AND CO.)]
[Illustration: RIPPLE MARKS ON A LAYER OF THE SHEPARD FORMATION NEAR
LOGAN PASS. THEIR ASSYMMETRICAL FORM INDICATES FORMATION BY CURRENTS IN
SHALLOW WATER.
(DYSON PHOTO)]
The Belt Formations
ALTYN FORMATION.
This is the oldest of the several formations and thus occupies a
stratigraphic position at the base of the entire series. It is composed
mainly of sandy dolomites (magnesian limestones) and limestones which
weather to a light buff color. It outcrops all along the base of the
eastern front of the Lewis Range and comprises the entire block of Chief
Mountain. Because of its comparatively great resistance to weathering
and erosion it usually forms a conspicuous ridge or terrace wherever it
crosses a valley. In the Swiftcurrent Valley it forms the dam which
holds in Swiftcurrent Lake and creates Swiftcurrent Falls. In Two
Medicine Valley the highway crosses a similar terrace which gives rise
also to Trick Falls. In the St. Mary Valley it creates the Narrows and
forms the imposing wall in lee of which East Glacier Campground is
located. The rock of this formation can best be examined on the ridge
immediately east of Many Glacier Hotel (between hotel and parking lot)
and above Swiftcurrent Falls. Its average thickness is about 2,300 feet.
APPEKUNNY FORMATION.
Lying on top of the Altyn are 3,000 or more feet of prevailing greenish
shales and argillites[2] comprising the Appekunny formation. Slabs of
these rocks, because of their great hardness, have been used as
flagstones in the walks at the Many Glacier Ranger Station and adjacent
Park Service residential area. Mud cracks and ripple marks are common.
The formation is prominent on the side of Singleshot Mountain near the
St. Mary entrance to the park, and everywhere immediately overlying the
lighter-hued Altyn along the east edge of the Lewis Range where,
especially when seen from a distance, it appears to have a purplish
color. It also outcrops along the western base of the Livingstone Range
(Figure 3D), but such exposures are as a rule obscured by a cover of
dense forest. Accessible outcrops can readily be examined along
Going-to-the-Sun Highway for several miles east of Sun Point and near
McDonald Falls, and also along the lower part of the Grinnell Glacier
trail.
GRINNELL FORMATION.
Because of their dominantly red color, the shaly argillites which
comprise the bulk of this formation are the most conspicuous rocks in
the park. They lie immediately on top of the Appekunny and although
their thickness varies considerably it is greater than 3,000 feet in
several localities. Interbedded with the red argillites are thin white
layers of quartzite, a former sandstone which has been converted by
pressure into an extraordinarily hard, dense rock. Mud cracks, ripple
and current marks, raindrop impressions, and other features made while
the sediments were accumulating are common. The red color is due to
abundant iron oxide occurring mainly as a cement between the sand and
mud grains. All the rocks of Glacier Park contain some iron, or rather
contain iron-bearing minerals. These minerals have various colors unless
they have been oxidized, in which case the color is red or brown.
Oxidation of the Grinnell formation probably took place while the mud
was accumulating and during those periods when it was exposed to the
atmosphere. At such times also the mud dried and cracked, the marks of
which are so prominent on the surfaces of the layers today.
The Grinnell formation seems to be everywhere. In the Many Glacier
region it comprises the bulk of Grinnell Point, Altyn Peak, and Mount
Allen, and is no less striking in the bases of Mount Wilbur and the
Garden Wall. Ptarmigan Tunnel is drilled through it, and the trails to
Grinnell Glacier, Cracker and Iceberg Lakes cross it. Redrock Falls, on
the trail to Swiftcurrent Pass, and Ptarmigan Falls on the Iceberg Lake
trail drop over several of its highly colored layers.
From the Blackfeet Highway on top of Two Medicine Ridge one can see the
dark red rocks of this formation capping the summits of Rising Wolf and
Red Mountains. Even from the valley floor it is just as noticeable.
Sinopah Mountain standing alone and impressive across the lake from Two
Medicine Chalets carries the red banner of the Grinnell formation.
These red rocks constitute an important scenic feature for many miles
along Going-to-the-Sun Highway. If one begins his trip on this highway
at its east entrance he soon finds himself in the midst of a group of
imposing red peaks—Goat and Going-to-the-Sun on the right, Red Eagle and
Mahtotopa on the left. The road crosses the formation along a mile and a
half stretch just west of Baring Creek bridge. Innumerable loose slabs
of red rock along the side of the road contain excellent mud cracks and
ripple marks. Near Avalanche creek on the west side of Logan Pass the
highway crosses the Grinnell where it comes to the surface on the
western limb of the big syncline.
The formation is well exposed in the vicinity of Sperry Chalet and
Glacier. It forms all the mountains surrounding the basin in which the
chalet is located, and the trail from chalet to glacier lies wholly on
it. At the glacier intensely folded white quartzite layers and red
argillites are very conspicuous.
The visitor can readily trace the Grinnell from place to place
throughout the entire park area, and can thus easily visualize that it
as well as all other formations at one time filled the intervening
spaces between the mountains. (See color of cover pages.)
SIYEH FORMATION.
Next above the Grinnell is a thick limestone formation which, because of
its weathered buff color, stands out in sharp contrast to the red beds
upon which it rests. It is the greatest cliff-maker in the park and in
several places its entire thickness of 4,000 feet may be exposed in a
single nearly vertical cliff. Since it is younger than the three
preceding formations, it is confined mainly to the higher elevations,
capping many of the loftiest peaks within the Lewis and Livingstone
Ranges. In the Many Glacier area such peaks are Mount Gould and the
Garden Wall, Mounts Siyeh, Grinnell, Allen, Wilbur, and Henkel. A number
of others, including Little Chief, Jackson, Gunsight, Fusillade,
Going-to-the-Sun, Piegan, Pollock, Cannon, and Heavens Peak, are visible
from Going-to-the-Sun Highway. The huge peaks—Kinnerly, Kintla, Carter,
and Rainbow—which stand guard at the heads of Kintla and Bowman Lakes
are composed of the Siyeh. The list also includes Cleveland, highest and
largest of all.
[Illustration: ALGAE COLONIES IN SIYEH LIMESTONE NEAR GRINNELL GLACIER.
(DYSON PHOTO)]
[Illustration: GENTLY TILTED STRATA OF THE SIYEH FORMATION IN GRINNELL
MOUNTAIN.
(DYSON PHOTO)]
Within the Siyeh there is a bed, averaging about 60 feet thick, composed
almost entirely of fossil algae which apparently formed an extensive
reef or biostrome on the floor of the shallow Belt Sea. The algae
colonies are in the form of rounded masses up to several feet in
diameter and bear a crude resemblance externally and internally to a
head of lettuce or cabbage. Geologists know these algae by the genus
name Collenia. Because of the rounded and smoothed surfaces on these
colonies, mountain climbers frequently find the reef difficult to cross.
It appears as a distinct light gray horizontal band on the east face of
Mount Wilbur about midway between the base of the cliff and the peak’s
summit, where it can easily be seen from Many Glacier Hotel and
Swiftcurrent Camp. It is also discernible on the Pinnacle Wall above
Iceberg Lake and in Mount Grinnell. The Swiftcurrent Pass trail crosses
it just east of the pass, and it is also exposed along Going-to-the-Sun
Highway below the big switchback on the west side of Logan Pass where
attention is directed to it by a sign. Unweathered portions of the reef
rock are light blue. A similar but thinner reef outcrops at Logan Pass
near the start of the Hidden Lake trail. Although most of the fossil
algae occur in the Siyeh they are present in the younger formations and
also in the Altyn. Other than algae the only undoubted fossils of the
Belt series within Glacier National Park are burrows probably made by
worms. They are rare and are restricted mainly to the Siyeh formation.
[Illustration: FOSSIL ALGAE IN SIYEH FORMATION, HOLE-IN-THE-WALL BASIN.
(THE ROCK BOOK BY C. L. FENTON AND M. A. FENTON, DOUBLEDAY AND CO.)]
At the top of the Siyeh are several hundred feet of sandy and shaly
beds, mostly reddish in color, grouped by some geologists into a
distinct formation known as the Spokane. At Logan Pass it is about 700
feet thick and is well exposed in the lower parts of Clements and
Reynolds Mountains, and at the site of the former “Clements” Glacier.
SHEPARD FORMATION.
Several hundred feet of limy beds which weather yellow-brown lie on top
of the Siyeh. Although named for outcrops on the cliff above Shepard
Glacier (south of Stoney Indian Pass and near the site of the old
Fifty-Mountain tent camp) the formation is exposed on the summit of
Swiftcurrent Mountain at the head of Swiftcurrent Valley, on Reynolds
and Clements Mountains near Logan Pass, and on Citadel and Almost-a-Dog,
visible from Going-to-the-Sun Highway in St. Mary Valley. The formation
is replete with mud cracks and ripple marks. Some rock surfaces exhibit
two and three sets of the latter.
KINTLA FORMATION.
These beds have the same bright red color as those of the Grinnell.
However, because they are the youngest rocks of the Belt series they
outcrop only on a few mountaintops, and inasmuch as these are mainly in
the northwest part of the park, comparatively few people have noticed
this formation. Visitors to Cameron Lake in Waterton Lakes National Park
can see it in the red north wall of Mount Custer. The mountains around
colorful Boulder Pass and Hole-in-the-Wall Basin are likewise composed
of it.
Within the rocks of this formation there is a great abundance of small
cubes believed to be casts of salt crystals which formed when the
sediments were accumulating. Their presence indicates an arid climate
and intensive evaporation of the sea, similar to the condition at Great
Salt Lake today.
Igneous Rocks of the Belt Series
Not all of Glacier Park’s rocks accumulated slowly and quietly as
sediment in a body of water. At many places, interbedded with and
cutting across the sediments, there are bodies of igneous rock which
reached their present position in the form of hot molten material forced
up from deep within the crust.
[Illustration: COLUMNAR SECTION OF BELT ROCKS]
PROTEROZOIC
KINTLA 860′+ Red argillite
SHEPARD 600′ Buff limestone
PURCELL 250′ Black lava
SIYEH 4000′ Dark diorite bordered by white altered
limestone
Blue limestone. Weathers buff
GRINNELL 1600-3000′ Red argillite and white quartzite
APPEKUNNY 2500′± Green argillite. Some white quartzite
ALTYN 2300′± Gray limestone. Weathers buff
PURCELL LAVA.
Soon after the youngest layers of Siyeh limestone had accumulated on the
floor of the sea and while they were still under water, a mass of molten
rock was squeezed up from far below and extruded in the form of a
submarine lava flow over the recently accumulated sediments. Several
times this lava poured out forming a total thickness varying between 50
and 275 feet. One of the best exposures is on the west side of
Swiftcurrent Pass and in Granite Park just west and northwest of the
chalet. In fact it is this lava flow which gives the name, albeit
wrongly, to Granite Park. The material of the flow is very fine-grained
and dark (basic), in contrast to the light color and coarse grain of
granite. Nonetheless, many prospectors are wont to call every igneous
rock, regardless of its composition, a granite. A number of ellipsoidal
structures (“pillows”) up to two feet in diameter within this lava
indicate that it was extruded under water. The Purcell is thickest in
the vicinity of Boulder Pass, where the trail traverses its ropy and
stringy surface for a distance of several hundred yards.
Later, after the Shepard and part of the Kintla formation were laid down
on top of the Purcell, another similar flow spread over the sea floor.
DIORITE SILL.
Few persons visit the park without noticing the pronounced black layer,
within the Siyeh formation, present on many of the high peaks. It is
most in evidence on the face of the Garden Wall viewed from the vicinity
of Many Glacier Hotel, although it is plainly visible also in Mount
Wilbur and the wall above Iceberg Lake. Passengers on the Waterton Lake
launch can see it cutting across the stupendous north face of Mount
Cleveland. From Going-to-the-Sun Highway it can be seen on Mahtotopa,
Little Chief, Citadel, Piegan, and Going-to-the-Sun Mountains, and on
the west side of the Garden Wall, where it also forms the cap of
Haystack Butte. It is everywhere about 100 feet thick, and thus can be
used as a very accurate scale for determining the height of mountains on
which it is discernible.
This imposing layer of rock, unlike the lava, never reached the surface
in a molten state, but was intruded between beds of sedimentary rock and
thus became a sill instead of a flow. We need only a glance to determine
its intrusive nature. Wherever it occurs it is bordered at top and
bottom by thinner gray layers. These are Siyeh limestone which was
changed to marble by the tremendous heat of the diorite during its
intrusion. This effect is termed contact metamorphism by geologists.
Because this contact-metamorphosed zone is at both top and bottom of the
sill we know the latter was intruded into the adjacent rocks. Lava
flows, even though covered later by sediments, of course alter only the
underlying rocks.
[Illustration: THE GARDEN WALL AND GRINNELL GLACIER. THE WALL IS
COMPOSED OF SIYEH LIMESTONE ABOVE THE LEVEL OF THE GLACIER AND THE
GRINNELL FORMATION BELOW IT.
(DYSON PHOTO)]
The sill can readily be examined in a number of places where trails
cross it, notably at Swiftcurrent and Piegan Passes, and north of
Granite Park near Ahern Pass. But nowhere is it as accessible as on
Logan Pass. It lies beneath the parking lot at a depth of only a few
feet, and is exposed on both sides of the pass. To inspect it, one need
walk only about 200 yards along the trail leading to Granite Park. In a
distance of less than 100 feet the trail traverses from fresh Siyeh
limestone across the entire altered (contact-metamorphosed) zone, here
12 to 20 feet wide, into the center of the sill. All parts of the sill
and adjacent rocks can readily be examined and studied in detail at this
site.
[Illustration: TOP OF THE DIORITE SILL OF BLACKFOOT GLACIER. THE MAN IS
STANDING ON THE SILL. LIGHT ROCK OVERLYING SILL IS CONTACT-METAMORPHOSED
SIYEH LIMESTONE.
(DYSON PHOTO)]
A number of dikes[3] of Belt age, some of which undoubtedly were feeders
to the sill and flows, cut vertically up through the sedimentary
formations. Some of the dikes are less resistant to weathering and
erosion than the rocks surrounding them; consequently their more rapid
removal results in the formation of narrow vertical chimneys or recesses
which appear as snow-filled chutes on the mountainsides in spring and
early summer. Such a feature almost invariably indicates the presence of
a dike. From Many Glacier Hotel one of these can be seen on the red
mountain in front of Mount Wilbur. Another, 1,500 feet high, transects
the Pinnacle Wall at the outlet of Iceberg Lake. The dike which forms
this impressive chute is less than thirty feet wide. Though not so
conspicuous as the sills some of these dikes are of interest because
they contain various ore minerals, principally copper, which today form
small deposits along their borders. About the beginning of the century
these were responsible for a short-lived mining boom, the best known
vestige of which is the remains of the mill at Cracker Lake. The old
Cracker Mine, with entrance now caved in, was driven along a dike which
has a width of over 100 feet.
From the boat landing at the head of Josephine Lake the dump of another
mine appears as a tiny gray-green mound on a narrow shelf high on the
precipitous wall of Grinnell Point. Like the Cracker Mine this one was
dug along the edge of a similar but smaller dike. All these deposits are
insignificant in size and of no commercial value. Had they been
important this great area might never have been set aside as a national
park.
[Illustration: MOUNT WILBUR AND THE PINNACLE WALL VIEWED FROM MANY
GLACIER HOTEL. THE UPPER PART OF APPEKUNNY AND ALL OF THE GRINNELL AND
SIYEH FORMATIONS ARE VISIBLE. THE SNOW-FILLED CHUTE LEFT OF THE WORD
“GRINNELL” IS FORMED BY THE SAME DIKE WHICH PASSES THROUGH THE PINNACLE
WALL.
(HILEMAN PHOTO, COURTESY GLACIER PARK CO.)]
The Story Continues
For the succeeding several hundred million years the geologic history of
Glacier National Park is rather obscure, but additional Belt sediments
apparently were deposited before uplift of the area caused the sea to
withdraw. Following this event many feet of the younger Belt sediments
were removed by erosion. The sea probably returned and received more
sediments during much of the Paleozoic Era, although no trace of these
rocks has been found inside the park boundaries.
CRETACEOUS ROCKS.
Not until the Cretaceous period of Earth history, about 100 million
years ago, did the geologic record again become clear. At that time a
great thickness of mud and sand was deposited in the geosyncline burying
deeply the ancient Belt and other rocks which had accumulated as
sediment during the preceding several hundred million years. Life had
made tremendous advances in this interval, and the abundance of fossils
in Cretaceous rocks indicates that the sea swarmed with shelled
creatures during that period.
THE LEWIS OVERTHRUST.
Toward the end of Cretaceous time tremendous crustal forces, principally
from the west, were directed against the geosyncline with the result
that its rocks were compressed and uplifted, converting the site of the
former sea into a mountainous region. Similar activity took place
throughout the length and breadth of the entire geosyncline, which
resulted in the formation of the Rocky Mountain system stretching
between Mexico and Alaska. A number of mountains were formed on other
continents during this period. So widespread and tremendous was the
deformation, especially in the present day Rocky Mountain region, that
it is known as the Rocky Mountain, or Laramide (after the Laramie Range
in Wyoming), revolution. Mountain-building forces continued for several
million years in the Glacier Park area, finally squeezing the rocks into
a great fold (anticline). Continued pressure from the west overturned
the fold and put additional strain on the rock layers, eventually
causing them to break along a great low-angle fault. The western limb of
the fold, now a great slice of the crust, was driven upward and eastward
over the eastern limb ultimately reversing the order of rock layers by
placing older on top of younger ones (Figure 3). These younger layers
are Cretaceous shales and sandstones underlying the plains immediately
east of the mountains. The mountains themselves have been carved by
streams and glaciers from the Belt formations comprising the upper block
of older rock, that slice of the crust which has been moved more than 15
miles toward the east. The surface over which it was pushed is the Lewis
overthrust. At the time this great break occurred the part of it now
exposed in Glacier National Park was deeply buried. It was long after
that when removal by erosion of overlying Belt rocks, possibly several
thousand feet of them, finally exposed the fault.
FIGURE 2. MAP OF WATERTON-GLACIER INTERNATIONAL PEACE PARK
LEGEND
1. TRACE OF LEWIS OVERTHRUST
2. ALLUVIAL FANS
3. RANGE CRESTS
4. HIGHWAYS
Movement along this fault was slow—so slow that had people been present
at the time they probably would not have been aware that anything of an
unusual nature was occurring. Occasionally along many large faults,
however, there is sudden movement of small magnitude, usually not more
than a few inches, but strong enough to vibrate the crust. These
vibrations are earthquakes, and their frequent occurrence in California
and elsewhere along the Pacific coast indicates the presence of numerous
active faults. Their occurrence also in the northern Rockies, as at
Helena, Montana in 1935 and 1936, attests to the fact that some of the
faults here are still active.
The Lewis overthrust comes to the surface at the base of the Altyn
formation along the entire precipitous east front of the Lewis Range and
can be traced nearly 100 miles northward into Canada and for almost an
equal distance south of the park. The section lying within the park is
tilted very gently toward the southwest, the angle of dip seldom
exceeding ten degrees. In some places it is practically horizontal. For
this reason the lower courses of all the largest, and some of the small,
valleys on the east side of the Lewis Range have been cut entirely
through the upper block (overthrust) of Belt rocks down into the weak
Cretaceous shales underneath. This causes the trace of the overthrust to
be very sinuous and also accounts for the deep indentations in the
mountain front formed by Swiftcurrent, St. Mary, Two Medicine, and other
valleys. The floors in the lower courses of these valleys, because they
lie below the level of the thrust surface, are composed of Cretaceous
shales. In most places these rocks are covered by glacial moraine, but
they are exposed along the highway from Babb into the Swiftcurrent
Valley, especially along the shore of Sherburne Reservoir and near the
entrance station. Because these shales readily disintegrate when exposed
to the atmosphere they give rise to slumps and landslides which,
although of small proportions, cause a great deal of damage to the
highway, sections of which must be rebuilt annually. At most damaged
spots along the route the shales appear as a dark mud or clay in the
roadcuts. The bumpy topography of the whole slope lying north of the
road has been formed by innumerable such small landslides.
A deep well located near Cameron Falls in Waterton Townsite (Waterton
Lakes National Park) about one mile west of the edge of the mountains
passes through 1,500 feet of Belt rocks and then penetrates the Lewis
overthrust and the Cretaceous shales beneath.
In the southern part of Glacier National Park just north of Marias Pass,
Debris Creek has cut a hole or “window” (known as a fenster by
geologists) through the overthrust block (Figure 2). Thus a small area
of Cretaceous rock completely surrounded by the Belt series lies within
the mountains. This is the only such Cretaceous outcrop in the park, but
like the well at Waterton, it serves as a reminder that the rocks of
this period are everywhere present under the mountains, and their
surface constitutes the “sliding board” over which the upper, more
massive block of Belt rocks was pushed. And so we see that the mountains
of Glacier National Park, unlike many of the world’s great ranges, have
no roots, for they rest on a base of greatly different and much less
resistant material, the Cretaceous shales. Presumably the Lewis
overthrust and Cretaceous rocks beneath it would be penetrated by a well
drilled anywhere within the mountains, although in the Livingstone Range
the depth of such a well would be very great (Figure 3D).
FIGURE 3. HISTORY OF LEWIS OVERTHRUST
A HYPOTHETICAL SECTION NEAR THE CLOSE OF CRETACEOUS TIME.
B PRESSURE FROM WEST CREATES LARGE FOLD AND OVERTURNS IT TOWARDS EAST.
THE NEW MOUNTAINS ARE CUT DOWN BY EROSION.
C CONTINUED PRESSURE BREAKS THE STRATA AND THE LEWIS OVERTHRUST IS
FORMED. DOTTED LINE SHOWS APPROXIMATE PRESENT OUTLINE OF
SURFACE
D SECTION ACROSS THE PARK SHOWING RELATIONSHIPS OF ROCK FORMATIONS AND
THE LEWIS OVERTHRUST
(VERTICAL SCALE GREATLY EXAGGERATED)
Erosion in the eastern part of the overthrust block, in addition to
producing its crenulated edge, has left several isolated remnants
(outliers) east of the main mass of the mountains. The best known of
these is Chief Mountain situated near the northeast corner of the park
several miles west of the Chief Mountain International Highway. It is a
mass of Altyn limestone rising vertically on its east, south and north
sides for a distance of 1,500 feet. The Lewis overthrust is well exposed
all around its base. Two smaller pinnacles immediately to the west are
similar outliers, and, like Chief Mountain, were once part of the main
mass of the Lewis Range (Figure 3D and cover sketch). Divide Peak, at
the west end of Hudson Bay Divide, is another outlier. It, too, is
composed entirely of the Altyn formation.
Although the Lewis overthrust is exposed in a great number of places
very few of these are easily accessible, and at only one does a trail
provide a close approach to the actual contact between Belt and
Cretaceous rocks. The latter site lies along Roes Creek only a few
hundred yards from East Glacier Campground. Before reaching the fault at
the base of a high cliff of Altyn limestone, the trail crosses several
outcrops of Cretaceous sandstone replete with fossil pelecypods (clams)
and gastropods (snails). The fault surface is covered by loose rock
where the trail crosses it, but on the opposite side of the stream a
zone of crushed Altyn limestone and Cretaceous shale is visible.
From U. S. Highway No. 2 just east of Marias Pass an excellent distant
view of the thrust may be obtained. About three miles to the north it
appears as a nearly horizontal line high on the side of Summit Mountain.
Above it is a vertical cliff in which white Altyn and red Grinnell are
prominent, and below is a gentler slope composed of gray-brown
Cretaceous shale.
Cretaceous rocks with relatively low resistance to Earth stresses, were
strongly crumpled and folded during the period of overthrusting. The
folded zone extends several miles eastward from the mountains (Figure 3
D), and may be seen to good advantage along Blackfeet Highway on the
north side of Two Medicine Ridge, where a series of thin shales and
sandstones has been squeezed into anticlines and synclines.
It is because of the Lewis overthrust that there are no significant
foothills on the east side of the Lewis Range. The fault has brought
into direct contact the massive and resistant Belt rocks which stand up
as mountains, and the relatively weak shales of the plains which are
carved into subdued landscape features by erosion.
[Illustration: LEWIS OVERTHRUST AT BASE OF MT. WYNN SEEN FROM HIGHWAY
EAST OF MANY GLACIER HOTEL. OVERTHRUST LIES AT BASE OF CLIFF. CRETACEOUS
ROCKS OUTCROP ON GENTLE SLOPE BELOW THRUST.
(DYSON PHOTO)]
After the Lewis overthrust had taken place, and probably following a
period of erosion, the western part of the block broke along a vertical
fault and sank several thousand feet. For a short period of time a lake,
in which clay was deposited, covered the floor of this depressed area.
The present valley of the North Fork of the Flathead River lies on this
downfaulted block (Figure 3D), and the western boundary of the
Livingstone Range marks the trace of the fault. Because the fault is of
the high-angle variety the front of this range is much straighter than
that of the Lewis Range which is formed by the notched eastern edge of
the relatively thin overthrust block. The Belton Hills and Apgar
Mountains near the park’s west entrance are isolated blocks separated
from the Livingstone Range by normal faults probably dating from the
time the North Fork Valley subsided.
The Effect of the Ice Age
In Miocene and Pliocene time the mountains were deeply eroded by
streams. It was during this time that Chief Mountain, Divide Peak, and
two smaller outliers, and the fenster along Debris Creek were formed.
All of the existing mountain valleys were cut out of the overthrust
block, although not to as great a depth as they have today. The time
required for their formation amounted to several millions of years. The
result of all this erosion was a landscape very similar to the present
day Blue Ridge in Virginia and North Carolina, the type which geologists
call mature.
Near the close of Pliocene time the climate cooled, timberline began to
lower, and increasing amounts of permanent snow accumulated in the
higher parts of the mountains. Finally glaciers formed from the snow and
began to move down the stream-carved valleys. This marked the advent of
Pleistocene time (The Glacial Age) nearly a million years ago. Glaciers
eventually filled all valleys and covered all the park area except the
summits of the highest peaks. Glaciers extended from valleys on the east
side of the Lewis Range far out onto the plains, and from the
Livingstone Range and the west side of the Lewis Range they moved into
the wide Flathead Valley. The forests disappeared and it is probable
that not a single tree remained in the area which is now the park.
Available evidence indicates that climatic fluctuations during
Pleistocene time caused the glaciers to disappear for a considerable
period of time, or at least to shrink to insignificant size and then to
return. At the end of Pleistocene time they began to shrink and about
9,000 years ago, during what is generally regarded as post-Pleistocene
time, disappeared again.
The large Pleistocene glaciers greatly altered the pre-existing
landscape of the park by gouging out valleys to much greater depth, and
making their sides and heads much steeper than the streams had been able
to cut them. Most of the lakes, vertical cliffs, sharp peaks, and
waterfalls which constitute much of the park’s magnificent scenery were
created as a result of intensive glacier action.[4]
The Last Chapter
Although events of the last 9,000 or so years didn’t create the large
spectacular features of the landscape, this period is nonetheless
interesting because it witnessed the birth of all existing park glaciers
and the return of the trees composing the present-day forests. As soon
as the glaciers began to shrink trees undoubtedly started to reclothe
the newly exposed surfaces. New varieties came from areas which had not
been glaciated. From the Pacific coast came grand fir, Douglas fir,
larch, hemlock, white pine and others. From the east came another group
including aspen, paper birch, hawthorn and maple. The native trees
driven out by the ice also returned to again become important elements
of the flora. These are Engelmann spruce, alpine fir, and lodgepole
pine. A few species, among which are the alpine willows, driven
southward from the far north during the Pleistocene period still persist
at high altitudes but they are always ready to move down into the
valleys if the climate should again become cool. Of course, continued
warming would cause them to disappear. After the large Pleistocene
streams of ice disappeared there followed a period of about 5,000 years
during which the climate was somewhat warmer and drier than at present,
conditions under which even very small glaciers could not have survived.
Then about 4,000 years ago the advent of the cooler climate brought
about the origin of the present glaciers. During the period of their
existence they have fluctuated in size, probably attaining maximum
dimensions around the middle of the last century. Since then they have
been steadily shrinking, a sure indication that the climate is becoming
milder, as it has so many times in the past.
[Illustration: MOUNT JACKSON, VISIBLE FROM GOING-TO-THE-SUN HIGHWAY, IS
COMPOSED OF STEEPLY TILTED STRATA OF THE SIYEH FORMATION. JACKSON
GLACIER TO THE LEFT OF THE MOUNTAIN LIES ON THE SURFACES OF SEVERAL OF
THESE STRATA.
(DYSON PHOTO)]
Surrounding all these small glaciers are recent moraines composed of
rock debris eroded from the basins in which glaciers lie. These moraines
thus represent the amount of material removed, and then deposited,
within the last 4,000 years. They are particularly striking at Grinnell
and Sperry Glaciers and at the site of the former Clements Glacier near
Logan Pass.
[Illustration: MORAINE NEAR GRINNELL GLACIER IS 120 FEET HIGH.
(DYSON PHOTO)]
Following disappearance of the large Pleistocene glaciers streams
returned to the valleys and began to cut new valleys within the old.
Because post-Pleistocene time has been of such short duration these new
valleys are small youthful gorges. Interesting examples are Sunrift
Gorge, where Baring Creek has cut a narrow channel into the upper part
of the Appekunny formation; and the gorge at Hidden Falls on Hidden
Creek in the Grinnell Valley. Sunrift Gorge lies only a few feet north
of Going-to-the-Sun Highway at Baring Creek bridge, and Hidden Gorge is
a stop on the guided trip which Ranger-Naturalists conduct from Many
Glacier Hotel to Grinnell Lake. Both of these channels have very smooth,
straight sides because they have been eroded along vertical fractures
known as joints. The latter are common throughout the mountains and are
responsible for the smooth surfaces on some of the highest cliffs. The
gorge of Avalanche Creek near Avalanche Campground is another example of
post-glacial stream erosion, only here the whirling action of sand and
gravel-laden water has carved out a number of cylindrical potholes in
the stream course. Some of them, though only 6 to 10 feet across, are 20
or more feet deep.
Since we know that the streams did not begin to cut these gorges until
the large Pleistocene glaciers had disappeared from those sites,
approximately 10,000 years have been required for their formation. Thus
the average maximum rate of down-cutting has been of the magnitude of
0.002 to 0.003 inch per year. With these figures as a foundation it is
not so difficult to comprehend that the much larger valleys of the park
could not have been eroded in less than several millions of years.
Another common, though seldom noticed, post-glacial feature of the park
is the alluvial fan. These are fan-shaped accumulations of gravel
deposited by swift, tributary streams where they enter a main valley.
Some of them have grown so large as to dam the stream in the major
valley and cause a lake (Figure 2). St. Mary, Lower St. Mary, Lower Two
Medicine, and Waterton Lakes are held in by such dams. The alluvial fan
of Divide Creek which holds in St. Mary Lake can easily be distinguished
from Going-to-the-Sun Highway on the north side of the lake near its
outlet. The St. Mary Entrance Station is located on this fan. The lower
lake is dammed by a large fan built into the St. Mary Valley by
Swiftcurrent Creek. The straight section of highway between the town of
Babb and the St. Mary River bridge lies on the lower part of this fan.
Inasmuch as the Pleistocene glaciers undoubtedly removed any such fans
made previously, those which are present today must have been
constructed since disappearance of the ice, and are then not more than
12,000 years old. Most of them are somewhat older, possibly by as much
as two or three thousand years, than the gorges mentioned above, because
the latter are located nearer the source of the glaciers, and their
sites were thus still covered by ice after the fans had already begun to
form. After the Pleistocene glaciers began their final retreat several
thousand years elapsed before they disappeared from the mountains.
[Illustration: FRONT OF LEWIS RANGE, NORTH SIDE OF SWIFTCURRENT VALLEY.
THE LEWIS OVERTHRUST LIES AT THE BASE OF THE CLIFF. THREE LARGE TALUS
CONES ARE VISIBLE BELOW MT. ALTYN ON THE LEFT.
(DYSON PHOTO)]
One of the most conspicuous of all post-glacial features is the talus
cone, an accumulation of angular rock fragments which fall from cliffs.
It is only at the base of a crevice or chimney that this material takes
the apparent form of a distinct cone. Elsewhere it is referred to as a
talus slope or simply as talus, or, in the parlance of some
mountaineers, as scree. Although several thousand years have been
required for their formation most talus accumulations in the park are
still actively growing, especially in spring and early summer when rocks
are pried loose by the alternate freezing and thawing of moisture within
fractures. The artillery-like crack made when a falling rock crashes to
the base of a high cliff is a familiar sound to anyone who has spent
much time in the mountains.
The Future
We know that the processes of erosion and weathering will continue, that
alluvial fans and talus cones will grow larger, and gorges will be
eroded deeper, and as a result the mountains will be cut down to lower
elevations. But, as we have seen, this event will require much time. If
the present climate continues for a few more years our remaining
glaciers will disappear, but there is nothing in geologic history which
says they won’t return again, possibly even to the size of their heyday
in the Pleistocene. And if history repeats itself, and all past geologic
history has been a repetition, then the mountains will eventually be
worn down to an uneventful plain and the sea will invade the land again.
But certain breeds of man are the only despoilers of mountains that we
need fear, so if the good citizens of our land keep the human invader
and his dams and earth-moving equipment out of our national parks these
grand mountains will endure for many thousands, yes, even millions of
years.
Footnotes
[1]Dr. Dyson worked as a ranger-naturalist in Glacier National Park for
eight summers starting in 1935.
[2]Argillite is the term used by geologists for a rock, originally a
shale, which has been recrystallized or made harder by greater
pressure. In external appearance it looks like shale.
[3]A dike is like a sill in all respects except that it cuts across
adjacent layers instead of paralleling them.
[4]For a complete discussion of glaciers and their effects see Special
Bulletin No. 2 (Glaciers and Glaciation in Glacier National Park) of
the Glacier Natural History Association.
PRINTED IN U. S. A.
BY
GLACIER NATURAL HISTORY ASSOCIATION
IN COOPERATION WITH
NATIONAL PARK SERVICE DEPARTMENT OF INTERIOR
1953
O’NEIL PRINTERS—KALISPELL, MONTANA
Principal Aims of the GLACIER NATURAL HISTORY ASSOCIATION, Inc.
Glacier National Park
West Glacier, Montana
Organized for the purpose of cooperating with the National Park Service
by assisting the Naturalist Department of Glacier National Park in the
development of a broad public understanding of the geology, plant and
animal life, history, Indians and related subjects bearing on the park
region. It aids in the development of the Glacier National Park museum
library, museums and wayside exhibits; offers books on natural history
pertaining to this area for sale to the public; assists in the
acquisition of non-federally owned lands within the park in behalf of
the United States government; and cooperates with government projects in
the completion and development of Glacier National Park as needed.
Revenue derived from the activities of the Glacier Natural History
Association is devoted entirely to the purposes outlined. Any person
interested in the furtherance of these purposes may become a member upon
payment of the annual fee of one dollar. Gifts and donations are
accepted for land acquisition or general use.
Bulletin No. 1—Motorists Guide to the Going-to-the-Sun Highway,
1947—Price 25 Cents.
Bulletin No. 2—Glaciers and Glaciation in Glacier National Park,
1948—Price 25 Cents.
Bulletin No. 3—Geologic Story of Glacier National Park, 1949—Price 25
Cents.
Bulletin No. 4—Trees and Forests of Glacier National Park, 1950—Price
50 Cents.
Bulletin No. 5—101 Wildflowers of Glacier National Park, 1952—Price 50
Cents.
Transcriber’s Notes
--Copyright notice provided as in the original—this e-text is public
domain in the country of publication.
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dialect unchanged.
--Only in the text versions, delimited italicized text (or
non-italicized text within poetry) in _underscores_ (the HTML version
reproduces the font form of the printed book.)
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