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Title: Field Book: Pennsylvanian Plant Fossils of Illinois - Educational Series 6
Author: Collinson, Charles, Skartvedt, Romayne
Language: English
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FOSSILS OF ILLINOIS ***
_Field Book_
PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS
Charles Collinson
Romayne Skartvedt
_Illinois State Geological Survey
Educational Series 6_
[Illustration: uncaptioned]
STATE OF ILLINOIS
DEPARTMENT OF REGISTRATION AND EDUCATION
First edition 1960
Reprinted 1966
ILLINOIS STATE GEOLOGICAL SURVEY
URBANA ILLINOIS
John C. Frye, Chief
Printed by Authority of State of Illinois, Ch. 127, IRS, Par. 58.25.
_Field Book_
PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS
Charles Collinson
Romayne Skartvedt
[Illustration: uncaptioned]
_Illustrations by Marie E. Litterer_
FOREWORD
[Illustration: Illuminated T]
This field book is intended to guide beginners in their collection and
general classification of plant fossils. It illustrates the plant
fossils most commonly found in Illinois and relates them to the plants
of which they were a part. A list of publications that will furnish more
detailed identification of specimens is included. The book has been
prepared in response to numerous inquiries to the Illinois State
Geological Survey from amateur collectors.
Information has been drawn from numerous sources. The works of Hirmer,
Janssen, Lesquereux, Noé, and Langford have been particularly useful.
We are especially indebted to Dr. Robert M. Kosanke, paleobotanist at
the Illinois State Geological Survey, and Dr. Wilson N. Stewart,
professor of botany of the University of Illinois, for helpful
suggestions and use of their libraries.
KEY TO PLANTS ILLUSTRATED ON TIME CHART
1. _Foerstia._ These fossils may be the earliest known occurrence of
bryophytes, although some authors have referred them to
the brown algae. After Dawson.
2. _Psilophyton._ A primitive vascular plant. After Dawson.
3. _Lepidodendron._ After Hirmer.
4. _Sigillaria._ After Hirmer.
5. _Calamites._ After Hirmer.
6. _Sphenophyllum._ After Fuller and Tippo.
7. _Equisetum._ The only living genus of scouring rushes. After Fuller
and Tippo.
8. _Megaphyton._ An ancient true fern. After Hirmer.
9. Modern tropical tree fern. After Fuller and Tippo.
10. _Medullosa._ An ancient seed fern. After Stewart.
11. _Williamsonia._ An extinct cycad-like tree. After Sahni.
12. _Cycas._ A modern cycad. After Chamberlain.
13. _Baiera._ A fossil leaf genus of ginkgo, whose only living
representative is the species _Ginkgo biloba_, saved from
extinction by careful cultivation in China. Several
specimens of this “living fossil” were presented to this
country by the Chinese and are now flourishing on many
college campuses, including that of the University of
Illinois. After Mägdefrau.
14. _Cordaites._ After Grand Eury.
15. _Lebachia._ A “transition conifer,” forerunner of present day
conifers. After Mägdefrau.
16. _Pinus._ Modern pine. After Mägdefrau.
17. _Acer._ Common maple, an angiosperm whose leaves are also found
among Tertiary fossils. After Mägdefrau.
18. _Rosa._ The prairie rose, an angiosperm.
19. _Campsis._ Trumpet vine, an angiosperm.
[Illustration: _Geologic Time Chart_]
_Time Units_
_Era and Years_
CENOZOIC “Recent Life”
Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
MESOZOIC “Middle Life”
Cretaceous
70 million
herbaceous lycopods
Jurassic
25 million
yellow-green algae
selaginellids
Triassic
30 million
cycad-like plants
Equisetum
PALEOZOIC “Ancient Life”
Permian
25 million
transition conifers
pines, spruces, firs, etc.
Equisetites
Pennsylvanian
25 million
ferns related to modern families
bryophytes
Mississippian
30 million
seed ferns
calamites
cycads
Devonian
55 million
cordaites
sphenophyllids
ancient ferns
Silurian
40 million
psitopsids
Foerstia
Ordovician
80 million
red algae
green algae
Cambrian
80 million
PROTEROZOIC _and_ ARCHAEOZOIC ERAS
4½ billion years
blue-green algae
chemosynthetic bacteria?
NO CERTAIN FOSSILS KNOWN
_Plants_
Algae
yellow-green algae
brown algae
red algae
green algae
blue-green algae
Mosses
bryophytes
Foerstia
Vascular Plants
“Whisk Ferns”
psitopsids
Club-mosses
scale and seal trees
quillworts
herbaceous lycopods
Scouring Rushes, Horsetails
Equisetites
Equisetum
calamites
selaginellids
Ferns and Seed Plants
Ferns
ancient ferns
ferns related to modern families
Gymnosperms
Cycads
seed ferns
cycads
cycad-like plants
Ginkgo
Conifers
cordaites
transition conifers
pines, spruces, firs, etc.
Flowering Plants
_Field Book_
PENNSYLVANIAN PLANT FOSSILS OF ILLINOIS
Charles Collinson and Romayne Skartvedt
[Illustration: Illuminated P]
Plants that flourished 200 million years ago have made Illinois one of
the best known fossil collecting sites in the world. The unusual
abundance and preservation of these fossils in the northern part of the
state have brought collectors to Illinois from many countries, and
prized specimens from that area may be seen in science museums
throughout the world.
The remarkable fossils represent plants that lived during the geologic
period called the Pennsylvanian or Coal Age and are the result of
special geologic conditions that occurred repeatedly during the period.
At the beginning of the Pennsylvanian Period, Illinois was part of a
vast lowland that stretched for hundreds of miles to the north, south,
and west, and was bordered on the east by highlands. At times much of
the plain was swampy and, because the climate was relatively warm and
moist, great jungles of fast growing trees, shrubs, and vines covered
the landscape. As successive generations of plants lived and died, plant
material fell into the swamp waters and, protected there from decay,
accumulated.
Frequently during the period, seas spread over the swampy lowlands,
submerging the forests and covering them with mud. Each submergence
lasted only a short time, geologically speaking. When the seas withdrew,
the deposits of sand and mud left behind were cut by streams that
carried fresh sand and mud from the eastern highlands. The streams
eventually became clogged with sediments and when the lowland was again
depressed swamp conditions returned and forests grew afresh. Such a
cycle of deposition was repeated again and again during Pennsylvanian
time, and after burial each layer of plant material gradually lost most
of its liquids and gases and was slowly converted into one of the
numerous coal beds presently found in Illinois.
[Illustration: Reconstruction of Pennsylvanian Coal-forming Swamp]
In some places in the state conditions existed that were especially
favorable for preservation of plants, and there delicately preserved
fossils are found in great numbers. In the most favorable areas, such as
in northern Illinois, the plants are preserved in stony nodules called
concretions, but they also may be found separately as molds, casts, or
petrifactions.
Molds (concave surfaces) and casts (convex surfaces) are fossilization
phenomena in which the actual plant, embedded in the surrounding
background rock, was dissolved, leaving a hollow space (mold) that
subsequently filled with other material. A cast was thus formed that
preserved the plant’s external features.
Most petrifactions are fossils in which silica, carbonate, or other
material permeated or replaced the internal structures of the plant and
preserved them so well that in most specimens the finest cellular
details can be observed. Compressions, another kind of petrifaction, are
the pressed carbonized remains of the plant itself.
PENNSYLVANIAN FLORA
[Illustration: _Aphthoroblattina_]
[Illustration: _Teneopteron_]
The far-reaching Pennsylvanian swamplands had abundant species of trees
and other plants that long since have become extinct. Today’s common
deciduous trees were not present; flowering plants had not yet evolved.
Instead, the tangled forests were dominated by giant ancestors of
presently existing club-mosses, horsetails, ferns, conifers, and cycads.
The undergrowth also was well developed, consisting mainly of ferns,
fernlike plants, _Sphenophyllum_, and small club-mosses. The plant
fossils give no indication of seasonal variations. The forests,
evidently always green, grew rapidly and abundantly, with foliage of
unprecedented size and luxuriance. Land animals were just beginning to
develop and included sluggish, salamander-like amphibians, large
primitive insects, and a few small reptiles. The insects flourished as
never before or since in the damp forests and attained remarkable size.
Insects more than four inches long were common and some are known to
have been more than a foot long with a wingspread proportionately broad.
Ancestors of the modern spiders, scorpions, centipedes (one fossil found
in Illinois was twelve inches long), cockroaches, and dragonflies are
represented by several hundred species.
The fossilized plants of Pennsylvanian time belonged to only a few main
categories: scale and seal trees, ancient scouring rushes (horsetails),
herbaceous _Sphenophyllum_, ferns, seed ferns, and cordaitean trees.
SCALE AND SEAL TREES
(Plate 1)
Scale and seal trees were abundant during the Pennsylvanian Period and
were important contributors to coal beds. Although distantly related to
the diminutive club-mosses and ground pines of the present, the trees
grew on straight, slender trunks to heights of more than a hundred feet.
[Illustration: Reconstruction of _Lepidodendron_
(after Hirmer)]
Scale trees were so called because their numerous, closely set, spirally
arranged leaves left scarred “cushions” on the branches and trunk,
making them appear scaly. Seal trees derived their name from the
signetlike appearance of their leaf cushions. The two best known types
belong to the genera _Lepidodendron_ (scale tree) and _Sigillaria_ (seal
tree), and fossils of both are common in Illinois.
_Lepidodendron_ had long, slender, somewhat tapering trunks. Some of the
trees reached heights of more than 100 feet and measured more than two
feet in basal diameter. The trunk ended in a spreading crown formed by
repeated dichotomous branching. The leaves were awl-shaped or linear,
ranging from one to 30 inches long.
The leaf cushions of _Lepidodendron_ are diamond-shaped, longer than
broad, and arranged in spiral rows around the trunk and branches. A
different name, _Lepidophyllum_, is used for fossils of the long,
bladelike leaf when it is found detached.
Spores were borne in long cylindrical cones at the tips of the branches.
Those cones referred, or assigned, to the genus _Lepidostrobus_ bore
both small spores (microspores) and large spores (megaspores) in the
same cones. Those in which only a large single spore, a somewhat
seedlike structure, was developed in a spore sac (sporangium) are
referred to the genus _Lepidocarpon_.
The rather commonly found genus _Stigmaria_ comprises so-called
“appendages” which, although stemlike in structure, apparently served as
roots for the scale and seal trees. These appendages are identified by
irregular spirals of circular scars (pits) that mark the attachment
points of former rootlets.
[Illustration: Reconstruction of _Sigillaria_
(after Hirmer)]
_Sigillaria_, although less common than _Lepidodendron_, was widely
distributed during the Pennsylvanian Period. It differed in growth habit
from _Lepidodendron_ in that it generally had fewer branches and not
uncommonly was unbranched. Some species also possessed a thicker trunk,
with hexagonal to elongate leaf cushions separated by vertical ribs. The
trunk was crowned, in the manner of the modern palm tree, by a cluster
of large, grasslike leaves.
The detached leaves of _Sigillaria_, extremely difficult to distinguish
from _Lepidophyllum_ (leaves of _Lepidodendron_), are referred to the
genus _Sigillariophyllum_ if preserved as compressions and to
_Sigillariopsis_ if preserved as petrifactions. Unbranched _Sigillaria_
trunks have been found that are more than 100 feet long and six feet in
diameter near the base, but the average height probably was closer to 50
feet.
[Illustration: Reconstruction of _Calamites_
(After Hirmer)]
Not all Pennsylvanian trees were large, however. Small forms are known,
including the important undergrowth genera _Lycopodites_ and
_Selaginellites_. In woody types the trunk consisted of an inner region
of conducting and supporting tissues, surrounding concentric cortical
layers, and an outer layer of corklike bark. Although the fossil
impressions of the various bark layers have been given separate generic
names, these are not commonly used.
SCOURING RUSHES
(Plate 2)
Although related to the small, inconspicuous horsetails of today, the
ancient scouring rushes of the Pennsylvanian Period grew to the size of
trees and were among the most widely distributed plant groups.
Some of these plants attained heights of 40 feet or more, but the
average was closer to 20 feet. The trunks were jointed and bore a whorl
of branches at the joints (nodes). Their small leaves also grew in
whorls at nodes along the smaller branches. Internodal regions were
ribbed in the same manner as present day horsetails. Fossils of the
trunks are assigned to the genus _Calamites_ and quite commonly are
preserved in sandstone and shale.
The leaf whorls are placed in the genus _Annularia_. One form commonly
found in Illinois has long, pointed, needlelike leaves and is given the
name _Asterophyllites_. _Calamostachys_, shown on plate 5, is one of the
most common calamite cones.
SPHENOPHYLLUM
(Plate 2)
The name _Sphenophyllum_ refers to both stems and leaves of this extinct
genus, which was related to the scouring rushes—note its resemblance to
_Annularia_.
A small herbaceous plant, _Sphenophyllum_ formed much of the swampy
undergrowth of the Pennsylvanian Period and is abundant among Illinois
fossils. It had a slender, ribbed stem bearing whorls of delicate,
wedge-shaped leaves, generally less than three-fourths of an inch long,
attached around the stem in multiples of three.
The cones of this group also are slender, delicate structures, bearing a
number of sporangia, and are correctly called _Bowmanites_, although
they also have been called _Sphenophyllostachys_. These fossil cones
frequently are found in Illinois.
_Sphenophyllum_ first appeared during the Devonian Period, some 300
million years ago, but did not become abundant until Pennsylvanian time.
The genus continued through the Permian but died out in Triassic time.
FERNS
(Plates 1 and 3)
True ferns, like those living in today’s woodlands, were common in the
Pennsylvanian forests. Some species attained heights of 30 to 40 feet.
Their fronds (compound leaves divided into segments or leaflets)
commonly were five to six feet long.
[Illustration: Portion of fern frond showing sori on lower side of
leaflets]
True ferns do not produce cones or seeds, but spores, which develop in
cases called sporangia. The sporangia frond showing are attached in
clusters (sori) to the lower side or margins of the leaves. In modern
ferns the sporangia may also occur on fertile spikes.
The shape and position of the sori are used to identify modern ferns,
but because leaves that bear sori (“fertile” leaves) are rare among
fossil specimens, the number, shape, and attachment of the leaflets and
the pattern of the veins are more commonly used for identification.
[Illustration: Reconstruction of _Megaphyton_
(after Hirmer)]
Because fossils of complete fern plants have not yet been found,
separate names have been adopted for detached leaves, stems, and other
parts. For example, the fossil stems of some Pennsylvanian ferns found
in Illinois have been referred to two genera, _Megaphyton_, whose leaf
attachment scars are arranged in two vertical rows, one on either side
of the stem, and _Caulopteris_, whose leaf scars are arranged in a steep
spiral that becomes progressively flatter upward until near the top they
appear to be whorled. When the stem is a petrifaction, with internal
structures preserved, it is called _Psaronius_. The fronds are referred
to a number of genera, but those most commonly found in Illinois are
_Pecopteris_, _Asterotheca_, and _Ptychocarpus_.
[Illustration: Venation of seed fern leaflets]
_Pecopteris_
_Asterotheca_
_Ptychocarpus_
SEED FERNS
(Plate 4)
Seed ferns resembled true ferns in general, but they produced seeds,
borne on modified leaves. Where spore sacs and seeds are absent, the
leaves of seed ferns are difficult to distinguish from those of spore
ferns, although individual seed fern leaflets, called pinnae, are
somewhat larger.
[Illustration: _Medullosa_ Reconstruction and original drawing by
Wilson N. Stewart]
Seed ferns included vinelike plants in the undergrowth and trees such as
_Medullosa_. Some tree genera were very tall, with trunks more than two
feet in diameter. Unlike the true ferns, still living today, seed ferns
declined steadily after the close of the Pennsylvanian Period and
finally became extinct during Jurassic time. During Pennsylvanian time,
however, they were much more numerous and varied than true ferns.
[Illustration: Venation of seed fern leaflets]
_Alethopteris_
_Odontopteris_
_Mariopteris_
_Neuropteris_
_Linopteris_
Most of the common seed ferns found as fossils in Illinois can be
referred to the following leaf genera: _Alethopteris_, _Neuropteris_,
_Odontopteris_, _Linopteris_, _Mariopteris_ (which may be a true fern),
_Cyclopteris_, and _Spiropteris_. _Cyclopteris_ includes circular leaves
that occurred at the base of leaves referable to _Neuropteris_.
_Spiropteris_ includes young leaves that had not yet uncoiled and may
belong to either true ferns or seed ferns.
CORDAITES
(Plates 1 and 2)
[Illustration: Reconstruction of _Cordaites_
(after Hirmer)]
Cordaitean trees, forerunners of modern conifers such as pine and
spruce, were important during the Pennsylvanian Period for they were
distributed throughout the world. These trees, among the tallest plants
of the time, sometimes grew more than 100 feet high.
The cordaitean trunk was unbranched for three-fourths of the height of
the tree and was topped by dense branches bearing large, simple,
straplike leaves spirally arranged. The leaves had closely set parallel
veins and measured from half an inch to three feet or more long.
Internally, the structure of the trunks was similar to that of modern
pine trunks. Casts of the pith are referred to the genus _Artisia_. The
seeds were borne in clusters on branches in leaf axils.
The _Cordaites_ were major contributors to some coal beds.
FRUITING BODIES
(Plate 5)
Fossils representing many kinds of plant reproductive structures are
found in Pennsylvanian rocks, but unfortunately most of them are not
attached to any identifiable part of the parent plant and they cannot be
assigned definitely to a particular plant. Such fossils are referred to
genera and species solely on the basis of their own characteristics,
although, as in other fossil classifications, such “form genera” are
presumed to be parts of, or related to, the plants with which they are
found in habitual association.
A few such fossils, fairly common in Illinois, are illustrated on plate
5 to show their general shape and size. When attached to an identifiable
leaf or leaflet, the seed is referred to as the seed of that leaf genus.
For example, _Holcospermum_, a radially symmetrical seed with ribs and
grooves, _Codonotheca_, a stalked, spore-bearing, lobed “cup,” and
_Neuropterocarpus_, a flask-shaped seed with longitudinal ribs and
grooves, all have been associated with _Neuropteris_, a leaf genus.
[Illustration: Mazon Creek Strip Mine Area Showing Distribution of
Spoil Heaps. The small circular areas represent waste from
underground mines.]
_Trigonocarpus_, commonly found as a cast of the internal part of a
seed, is a trimerously symmetrical body frequently associated with
_Alethopteris_. _Pachytesta_ includes preserved structures and outer
layers of a seed. _Carpolithes_ is a catch-all “genus” functioning as a
general term for seeds and seedlike forms whose plant group affinities
cannot be determined.
COLLECTING AREAS FOR PENNSYLVANIAN PLANTS
Northern Illinois
Plant fossils can be found in almost any northern Illinois area where
Pennsylvanian rocks are exposed (see back cover), but in some places
they are much better preserved and more numerous than in others. Most of
the well known collecting areas and a few of the lesser known ones are
discussed below. Even though some of the localities were discovered many
years ago, they may indicate areas that are still favorable for
collecting.
Mazon Creek Area
Of all the fossils that have been found in Illinois, the most famous are
the plant remains from the world-renowned Mazon Creek area in the
northeastern part of the state. In this area in Grundy and Will
Counties, plant fossils are found in ironstone concretions in the lower
part of the Francis Creek Shale directly overlying the Colchester (No.
2) Coal.
Fossils were discovered in outcrops along Mazon Creek more than a
century ago and collections later were made from scores of conical spoil
heaps at underground mines. After coal stripping began in the 1920’s,
great numbers of specimens were collected.
In the stripping operations, the concretion-bearing beds are commonly
the last to be placed on the spoil heap. Weathering softens and removes
the shales and leaves the nodules concentrated on the surface. Each
season brings a new crop of concretions to the surface.
[Illustration: _Plate 1_]
_Calamites_ ⅓×
_Stigmaria_ ⅖×
_Lepidodendron_ ⅖×
_Calamites_ ¹/₁₀×
Fern Stem ⅔×
_Caulopteris_ ¼×
_Sigillaria_ ⅖×
_Megaphyton_ ⅗×
_Calamites_ ⅗×
_Artisia_ ⅗×
_Sigillaria_ sub-bark ⅗×
[Illustration: uncaptioned]
The concretions generally are oval to elongate and range from less than
an inch to a foot or more in maximum dimension. Only about one nodule in
ten contains plant remains.
Approximately 25 to 30 species have been found in this region. The
productivity of the area was shown by George Langford, Sr., a well known
midwestern fossil collector. He and his son split about 250 thousand
concretions during a 140-day period and obtained some 25 thousand plant
specimens. Fine specimens still can be collected in a few hours.
The plant collecting localities in Will and Grundy Counties along Mazon
Creek, four to six miles southeast of the town of Morris, were the first
to be well known. Ferns are especially abundant. Fossils of insects,
crustaceans, worms, and salamanders also have been found. Collecting
conditions vary considerably from season to season, and fossils are not
as easily obtained there as from the strip-mine spoil heaps.
Fossiliferous concretions may be found in a number of the strip mines in
the area, although probably most have come from the Northern Illinois
Coal Corporation mine between the towns of Braidwood and Wilmington.
In earlier years good collections were made from the spoil heaps of
underground mines. Especially notable are the mine dumps of the
Wilmington Star No. 7 mine, 2¼ miles west of Coal City, and Skinner No.
2 mine, two miles northeast of Braidwood.
In the vicinity of Morris on the northwest edge of the Mazon Creek area,
fossil ferns have been found along the north side of the Illinois River
and in the banks of the Illinois-Michigan Canal. About a mile north in
an area of strip mining, fossil-bearing concretions have been found in
shale and irregular sandstone layers.
[Illustration: uncaptioned]
[Illustration: _Plate 2_]
_Sphenophyllum_ ⅗×
_Lepidostrobophyllum_ ⅗×
_Annularia_ ⅗×
_Sphenophyllum_ 1×
_Lycopodites_ ⅗×
_Cordaites_ ⅗×
_Asterophyllites_ ⅓×
Fossils in concretions also have been collected from a shaly limestone
at the south end of the Kankakee River bridge along the Grundy and Will
county line.
Bureau County
Some 40 miles downstream from Morris on the Illinois River, plant
fossils have been discovered in waste from the Spring Valley Coal Co.
mine 1. They also are found in black shale below the LaSalle Limestone
in a small gully in the southwest part of town, but at neither place are
they plentiful.
Knox County
A notable number and variety of well preserved plant fossils have been
produced from a locality along Court Creek in East Galesburg. The Rock
Island (No. 1) Coal is mined in the area and the fossils appear to have
come from the shale overlying it.
[Illustration: uncaptioned]
Fossil plants also have been found in shales above the Colchester (No.
2) Coal in the vicinity of DeLong and with the Herrin (No. 6) Coal in
mines southeast of Victoria.
Mercer and Warren Counties
In northern Warren and southern Mercer Counties the sandstone underlying
the Rock Island (No. 1) Coal is termed the “Stigmarian” sandstone
because of numerous siliceous casts found in the bed. Many of the
fossils have been collected from an old mine dump and from ravines along
the Edwards River northeast of Aledo.
A number of representatives of _Sphenophyllum_, _Neuropteris_, and
_Annularia_ have been collected from ironstone concretions occurring in
shale that overlies the Colchester (No. 2) Coal about three miles
southwest of Alexis. They were found in a gully about a third of a mile
southeast of Center School.
[Illustration: uncaptioned]
[Illustration: _Plate 3_]
_Pecopteris_ 1×
_Ptychocarpus_ ⅗×
_Pecopteris_ ⅗×
_Mariopteris_ ⅗×
_Asterotheca_ ⅗×
_Spiropteris_ ⅗×
_Pecopteris_ ⅗×
In the same general area but about three miles due south of Alexis,
fossil plants also may be found in the clay pits of the Hydraulic-Press
Brick Company and the Northwestern Clay Manufacturing Company.
Fulton County
Although there are numerous isolated occurrences of plant fossils
throughout the extensive strip mines and outcrops in Fulton County, no
exceptionally good collecting localities have been discovered.
Fern and cordaitean leaves have been collected along Mill Creek about a
mile northeast of Pleasantview where the fossils occur in the shale
overlying the Babylon Coal. In the same general area, impressions and
casts of _Stigmaria_, _Lepidodendron_, and _Cordaites_ have been found
in the Babylon Sandstone.
[Illustration: uncaptioned]
Three miles north of Pleasantview, a quarter of a mile northwest of
Union School, several species of leaves have been collected from the
Browning Sandstone where it is exposed in a roadcut.
Farther east, there is a fairly good locality in the stream bluff of
Kerton Creek about 3¼ miles north and a quarter of a mile west of Bluff
City. There the plants are found about 18 feet below a coal bed.
Numerous fern impressions also are found in shale beds above the Herrin
(No. 6) Coal along the Middle Branch of Copperas Creek, six miles west
of Glasford. Other specimens may be found in these beds elsewhere in the
area.
McDonough County
[Illustration: uncaptioned]
In some of the small underground mines near Colchester, the shale
overlying the Colchester (No. 2) Coal contains ironstone concretions
similar to those from northeastern Illinois. More than 50 species of
plant fossils have been reported, but they were collected many years ago
from spoil heaps at the mines. Beds of the same age crop out widely in
other localities in western Illinois and may contain plant fossils.
[Illustration: _Plate 4_]
_Sphenopteris_ ⅗×
_Linopteris_ ⅗×
_Neuropteris_ ½×
_Odontopteris_ ⅗×
_Cycopteris_ ½×
_Alethopteris_ ⅗×
_Alethopteris_ ⅗×
_Odontopteris_ ½×
_Alethopteris_ ⅗×
Vermilion County
In outcrops about three miles below Georgetown on the Little Vermilion
River, a number of fossil plant species and one insect species have been
collected from shales overlying the Herrin (No. 6) Coal, locally called
the Grape Creek Coal. The fossils occur in concretions much like those
from Mazon Creek.
An occasional stem replacement or impression is found in the
concretionary shale above the No. 7 Coal in the strip mine area west of
Hillery. In fact, isolated fragmentary plant specimens are fairly common
in the Danville mining area, but no especially productive localities
have come to light.
Other Northern Illinois Localities
In addition to the counties listed above, a number of others have
produced plant fossils. For example, there are records of plant fossils
found southeast of Franklin in Morgan County, at Neelys in Peoria
County, and at a number of places in the southern and western parts of
Rock Island County. Local exploration is certain to turn up numerous
other collecting places at present unknown.
[Illustration: uncaptioned]
[Illustration: _Plate 5_]
_Codonotheca_ ⅗×
_Calamostachys_ 1×
_Pachytesta_ ⅗×
_Codonospermum_ ⅗×
_Cordaicorpus_ ⅗×
_Samaropsis_ ½×
_Whittleseya_ 1×
_Trigonocorpus_ ¼×
_Holcospermum_ ⅗×
_Neuropterocarpus_ ⅗×
_Lepidostrobus_ ⅗×
_Carpolithes_ ⅗×
Southern Illinois
[Illustration: uncaptioned]
Lawrence County
Near the Lawrence-Richland county line, not far from the towns of
Berryville and Calhoun, there is an area rich in the fossil
petrifactions called “coal balls” in which cellular structures of stems
and roots generally are well preserved.
Saline, Pope, and Johnson Counties
Saline County has more recorded plant fossil localities than any other
southern Illinois county. Fossil plant collecting localities are
isolated but numerous in the area southwest of Harrisburg. Mine dumps,
such as in the area five or six miles northwest of Eddyville, and many
outcrops are available throughout the region. The fossils probably are
associated with the Murphysboro, Delwood, Willis, Reynoldsburg, and
Battery Rock Coals.
One especially good collecting area is on the south tributary of the
East Branch Cedar Creek about 6½ miles south of Stonefort. The fossils
are found in six feet of shale overlying the Battery Rock Coal horizon.
Perry and Jackson Counties
Near DuQuoin and Murphysboro, a variety of well preserved plant fossils
has been collected from shales overlying both the Herrin (No. 6) Coal
and the Murphysboro Coal. Nearly all have come from shaft mines that are
not easily accessible to the collector.
One currently good outcrop locality for collecting plant fossils from
the shale above the Murphysboro Coal is just southeast of Murphysboro.
Other Southern Illinois Localities
Other collecting localities have been recorded west of McLeansboro in
Hamilton County, northwest of Mt. Vernon in Jefferson County, near
Grayville in White County, and in the Friendsville area of Wabash
County. There is no doubt that careful search will turn up many more.
Almost anywhere in the large coal producing areas of southern Illinois
plant fossils can be found either in spoil heaps or in outcrops along
stream, road, and railroad cuts. The thick Pennsylvanian sandstones that
crop out in a belt extending through Gallatin, Saline, Williamson, and
Jackson Counties generally contain compressions or replacements of
trunks or other woody plant parts.
SUGGESTIONS FOR COLLECTING PENNSYLVANIAN PLANTS
Where to Look for Plant Fossils
Pennsylvanian plants are most commonly found in shales directly
overlying coal beds. The shales are believed to be of nonmarine origin
like the coals and may contain fossils either in ironstone concretions
or on the bedding planes. The shale layers as well as the concretions
should be examined. Where the bed directly overlying the coal consists
of black slaty shale or limestone containing marine fossils, plant
remains are rarely abundant or well preserved.
Beneath the coals there generally is an underclay that is interpreted as
the material in which the coal forest grew. The underclay is in turn
underlain by a sandstone, and both are believed to be mostly nonmarine.
Stigmarian axes and “roots” are common in many of the underclays. Plant
fossils are common in the sandstone but generally are poorly preserved,
except in the local shaly lenses.
The best place to look for plant fossils in northern Illinois, except
for the strip mines of the Mazon Creek area, is probably in the spoil
heaps from shaft mines. The Colchester (No. 2) Coal has been extensively
mined by the longwall method. This technique causes the mine roof to
settle when the coal is removed, and the haulage ways are kept open by
removing the roof shale. Inasmuch as the roof shale is the Francis Creek
Formation of the Mazon Creek area, it may contain abundant plant-bearing
concretions. The shale is not everywhere fossiliferous, however, and in
many spoil heaps fossils are rare.
[Illustration: Tools for Collecting]
Collecting Equipment
The collector of plant fossils should have the following tools and
equipment:
① Hammer—a bricklayer’s hammer will work well.
② One or two chisels, preferably one large and one small.
③ Knapsack or basket in which to carry specimens.
④ Newspapers and a roll of tissue paper for protecting fragile
specimens.
⑤ Pencil and paper for labeling specimens and making notes about the
collecting locality from which the fossils came. Much of
the value of a particular fossil lies in knowing precisely
where it was found and the layer of rock it came from.
Rules of Courtesy
When entering a collecting area every collector should observe several
rules carefully:
① For your own protection get permission to enter and collect on any
private property. Such action also will help to assure your welcome if
you wish to come back again.
② Leave the gates exactly as you find them, open or closed. Do not climb
fences that may break or sag under your weight; crawl under or go
around.
③ Don’t litter, even though far from any house or other buildings. Do
not disturb the owner’s equipment, stock, or planted areas.
Handling Specimens
[Illustration: uncaptioned]
The most successful way to split an ironstone concretion is to set it on
edge, long axis horizontal, on any fairly large rock and strike the
upper edge with the hammer. If the concretion is one that developed
around a fossil nucleus, it generally will split along the plane of
weakness, revealing the fossil. Sometimes one side of the concretion
will break off in the middle, in which case the remainder should be
tapped firmly but gently on the upper edge until the fossil is
completely uncovered. Pieces of the broken half should be glued together
neatly with waterproof cement so that the entire specimen can be
retained.
Fossils embedded in shale may be recovered by the same method or by
repeatedly tapping a chisel inserted along the bedding plane. If the
fossil is exposed, the matrix can be chiseled away by slow, painstaking
effort.
The usual method of wrapping plant-bearing nodules is to place the end
of a sheet of newspaper between the two halves of the nodule, fold the
paper over the nodule, and roll it up in the sheet.
[Illustration: How to Wrap a Fossiliferous Concretion]
When several localities are visited in one collecting trip, the fossils
from each should be kept separate; cloth bags are convenient for this
purpose. Notes about the locality should be put in the same bag as
fossils from that locality so that there is no possibility of confusion.
Some fossils are so fragile or porous that they should be covered with a
hardening protective coat of crude gum arabic solution. (Refined gum
arabic will not serve.) This may be applied with a fine brush in
successive layers, or sturdier fossils may be dipped in it.
When a fossil is so delicate that the surface tension of the gum arabic
solution causes the fossil to “spread,” celluloid (not plastic)
dissolved in acetone should be substituted. Before this solution is
used, the specimen must be completely dry or the coating will become
cloudy or opaque.
If the specimen is pyritized, it should be sprayed with lacquer or
shellac to prevent disintegration. If these protective sprays are used
they must be applied to dry specimens during dry weather or the coating
will remain sticky.
[Illustration: uncaptioned]
REFERENCES
AN INTRODUCTION TO PALEOBOTANY. C. A. Arnold. McGraw-Hill Book Co., New
York, 1947, 433 p.
GRUNDY AND WILL COUNTIES. Frank H. Bradley. In Worthen et al., Geology
and Paleontology, Geological Survey of Illinois, vol. IV, 1870, p.
190-225.
PALMLIKE PLANTS FROM THE DOLORES FORMATION (TRIASSIC), SOUTHWESTERN
COLORADO. Roland W. Brown. United States Geological Survey Professional
Paper 274-H, 1956, p. 205-209.
CARBONIFEROUS INSECTS FROM THE VICINITY OF MAZON CREEK, ILLINOIS. F. M.
Carpenter. Illinois State Museum Scientific Paper 3, pt. 1, 1943, p.
7-20.
THE LIVING CYCADS. C. J. Chamberlain. University of Chicago Press,
Chicago, 1919, 172 p.
GUIDE FOR BEGINNING FOSSIL HUNTERS. Charles Collinson. Illinois State
Geological Survey Educational Series 4, 1956, 36 p. (Revised 1959, 40
p.)
HISTORICAL GEOLOGY. Carl O. Dunbar. John Wiley & Sons, Inc., New York,
1949, 576 p.
COLLEGE BOTANY. Harry J. Fuller and Oswald Tippo. Henry Holt & Co., New
York, 1954, 993 p.
HANDBUCH DER PALÄOBOTANIK, BD. 1: _THALLOPHYTA, BRYOPHYTA,
PTERIDOPHYTA_. Max Hirmer. R. Oldenbourg, Munich and Berlin, 1927, 708
p.
SOME FOSSIL PLANT TYPES OF ILLINOIS. Raymond E. Janssen. Illinois State
Museum Scientific Paper 1, 1940, 124 p.
LEAVES AND STEMS OF FOSSIL FORESTS. Raymond E. Janssen. Illinois State
Museum Popular Science Series; v. 1, 1957, 190 p.
THE MAZON CREEK EURYPTERID: A REVISION OF THE GENUS _LEPIDODERMA_. Erik
N. Kjellesvig-Waering. Illinois State Museum Scientific Paper 3, no. 4,
1948, p. 3-46.
PLANTS OF THE PAST. F. H. Knowlton. Princeton University Press,
Princeton, N. J., 1927, 275 p.
THE WILMINGTON COAL FLORA FROM A PENNSYLVANIAN DEPOSIT IN WILL COUNTY,
ILLINOIS. George Langford. Esconi Associates, Downers Grove, Ill., 1958,
360 p.
THE MAZON CREEK, ILLINOIS, SHALES AND THEIR AMPHIBIAN FAUNA. R. L.
Moodie. American Journal of Science, 4th Series, v. 34, 1912, p.
277-285.
INTRODUCTION TO HISTORICAL GEOLOGY. Raymond C. Moore. McGraw-Hill Book
Co., Inc., New York, 1958, 656 p.
PENNSYLVANIAN FLORA OF NORTHERN ILLINOIS. A. C. Noé. Illinois State
Geological Survey Bulletin 52, 1925, 113 p.
PENNSYLVANIAN INVERTEBRATES OF THE MAZON CREEK AREA, ILLINOIS. Eugene S.
Richardson, Jr. Fieldiana: Geology, v. 12, 1956, p. 1-76.
REPORT ON THE CARR AND DANIELS COLLECTIONS OF FOSSIL PLANTS FROM MAZON
CREEK. Wilson N. Stewart. Illinois Academy of Science Transactions, v.
43, 1950, p. 41-45.
A RECENTLY DISCOVERED _PHLEGETHONTIA_ FROM ILLINOIS. W. D. Turnbull and
Priscilla F. Turnbull. Fieldiana: Zoology, v. 37, 1955, p. 523-535.
[Illustration: uncaptioned]
EDUCATIONAL EXTENSION PROGRAM
The Educational Extension Section of the Illinois State Geological
Survey reaches the public through a number of channels, including
nontechnical publications, rock and mineral collections for Illinois
schools and educational groups, lectures, exhibits, correspondence
involving identification of rocks and minerals, news items for the
press, and field trips.
During each year six field trips are given, in widely separated parts of
the state, for teachers, students, and laymen. The general program is
especially designed to assist in teaching geological sciences and to
help make Illinois citizens aware of the state’s great mineral wealth.
Illinois State Geological Survey
Urbana, Illinois
[Illustration: ILLINOIS, Land of Lincoln]
[Illustration: PENNSYLVANIAN OUTCROP AREA]
Morris
Braidwood
Peoria
Colchester
Danville
Springfield
Duquoin
Murphysboro
Harrisburg
Marion
_Illinois State Geological Survey
Educational Series 6_
Transcriber’s Notes
—Silently corrected a few typos.
—Retained publication information from the printed edition: this eBook
is public-domain in the country of publication.
—In the text versions only, text in italics is delimited by
_underscores_.
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