collection which furnishes 15 species of fossil mammals. This was made
some time before 1883 by Hon. William McAdams, of Alton. It was briefly
mentioned by him at the Minneapolis meeting of the American Association
for the Advancement of Science in 1883 (Proceedings, vol. XXII, p. 268).
Apparently the collection was secured for the U. S. Geological Survey by
Professor O. C. Marsh and remained at Yale University until after his
death. The species were described by the writer in 1920 (Proc. U. S.
Nat. Mus., vol. LVIII, pp. 109–117). This collection seemed especially
valuable because the species were found inclosed in supposed nodules of
loess. In our country the loess has furnished few such remains. The
following is the list of the species as determined. Those marked by a
dagger are extinct.
†Megalonyx jeffersonii (p. 33).
†Equus sp. indet. (p. 187).
†Platygonus cumberlandensis? (p. 219).
†Sangamona fugitiva.
†Cervalces roosevelti?.
†Rangifer muscatinensis? (p. 246).
†Taurotragus americanus.
†Symbos cavifrons (p. 254).
†Bison sp. indet. (p. 259).
†Mammut americanum (p. 102).
Castor canadensis.
Marmota monax.
†Castoroides ohioensis (p. 279).
Geomys bursarius.
Ursus americanus.
Of these 15 species at least two-thirds are now extinct. This large
number might appear to indicate that the time of their existence was
rather early in the Pleistocene. However, it is quite certain that the
loess belongs somewhere about the middle of the Pleistocene; and there
are no species that require an earlier date.
After the writer’s descriptions of the fossils had been published, an
important paper on the geology of the locality was issued (Jour. Geol.,
vol. XXIX, 1921, pp. 505–514) by Professor Morris M. Leighton, who had
been commissioned by the Illinois Geological Survey to visit and study
the deposits involved. With the aid of Mr. John D. Adams, son of the
collector of the mammalian fossils, Professor Leighton succeeded in
finding the quarry in which most of the fossils had been collected.
At one quarry in Alton Professor Leighton obtained the following
geological section, the description of which is here somewhat abridged:
_Feet._
Soil loessial, dark brown, leached 1
Loess, brown above, grading below into buff, leached 4 to 5
feet, maximum thickness 20
Loess distinctly more reddish than that above; many fossil
snails, thickness about 30
Glacial till, reddish, with pebbles of Canadian rocks; more
oxidized than overlying loess; thickness 1–3
Mississippian limestone, about 100
The concretions which hold the mammalian fossils were found to lie
between the upper surface of the till and the overlying loess;
occasionally a concretion bears a drift pebble. The concretions have
resulted from the lime which in solution was brought down from the loess
and again precipitated so as to cement the loess materials around the
fossils.
Professor Leighton was not able to determine definitely the ages of the
till and of the two deposits of loess. As to the till, its geographic
location suggested that it belonged to the Illinoian, but it had many of
the characteristics of the Kansan. The latter is believed to be present
at St. Louis and other localities not far away. Before the overlying
reddish loess had been deposited the till had suffered weathering and
erosion, indicating a considerable lapse of time had intervened. The
lower reddish loess presented many evidences that it is a deposit
distinct from the upper buff loess; and there seemed to be some
indications of at least a short interval between them. Leighton’s
conclusion was as follows:
If the drift is Kansan in age, the reddish loess may be Sangamon; if, on
the other hand, the drift be Illinoian, the reddish loess probably is
Peorian. It is unlike any Peorian loess of which the writer knows, but
the color does not necessarily preclude that possibility.
As to the upper loess, Leighton thought it might be of early Peorian
age, but possibly of early Wisconsin. However, his final conclusion was
thus expressed:
“If the till proves to be Kansan in age, the weathering of the drift
may be credited to the Yarmouth interglacial epoch, the mammalian
fauna to late Illinoian or early Sangamon times, the reddish loess
probably to the Sangamon, and the buff loess to the Iowan....
However this may be, the Illinoian and Sangamon epochs are
post-mid-Pleistocene from the standpoint of duration of the
Pleistocene and the fauna represented by the McAdams collection may
be regarded as post-mid-Pleistocene.”
WISCONSIN.
The greater part of this State is covered by the drift-sheet which has
derived its name from the State, but in the southwestern corner is a
considerable tract which has never been subjected to glacial action. A
small part of this area extends southward into Illinois and another part
into northeastern Iowa. In Wisconsin it reaches eastward to Baraboo.
East of this driftless area is a tract lying along the southern border
of the State and reaching eastward about to 88° 40′ longitude, which is
covered by the Illinoian drift.
The most detailed geological survey of any part of Wisconsin, so far as
regards the Pleistocene, is that made by Dr. W. C. Alden, of the U. S.
Geological Survey, of the area comprised between the boundary of the
State on the south and 44 degrees of latitude on the north and between
Lake Michigan on the east and 90 degrees of longitude on the west. On
the western side it joins the Mineral Point Quadrangle, to be mentioned
further along. There is, therefore, a wide strip surveyed across the
whole State. The area treated by Alden is, of course, nearly entirely
covered by Wisconsin drift. In the southwestern corner a considerable
part of the driftless region is included. East of this, as already
stated, is a tract which the Wisconsin ice-sheet did not reach and which
shows Illinoian ground moraine and some terminal moraines of Illinoian
drift. This narrows as it approaches its eastward limit.
Alden (p. 166) informs us that at no place in the area subjected to
vigorous glaciation by the Wisconsin ice-sheet had soils or vegetal
deposits been found between the Wisconsin drift and the earlier drifts.
At several places, however, deposits have been discovered which probably
belong to earlier glacial stages. Just outside the area mapped by Alden,
in Calumet and Outagamie Counties, Lawson (Bull. Wis. Nat. Hist. Soc.,
vol. II, pp. 170–173) has recorded the discovery of much wood and other
vegetable matter. Baker (“Life of the Pleistocene,” p. 317) has referred
the deposits to the Sangamon. These interglacial deposits of uncertain
age need not be here noted further. In this Wisconsin area some remains
of mastodons and elephants have been met with, but all are relics of a
time after the partial or complete recession of the Wisconsin glacier.
Remains of two individuals of _Elephas primigenius_ have been found in
Milwaukee (p. 143). It is evident that they lived there after the
withdrawal of the Wisconsin ice-sheet. One of these was buried beneath
peat and clay at a depth of 10 feet or more and at a level of about 100
feet above the present level of Lake Michigan.
At Dover, in Racine County, in 1878, a proboscidean tusk and some bones
were found in a peat-bog. They have been identified as those of a
mastodon, but of this one can not be certain. The age of the deposits is
that of the Late Wisconsin stage, after the withdrawal from that
vicinity of the ice, but how long after one can not say. The Milwaukee
Public Museum has a tooth of a mastodon (p. 111), labeled as found at
Waukesha. Its geological age is that of the other remains here referred
to. In the collection of the University of Wisconsin is a large vertebra
of a proboscidean which was found in Lake Monona. Its time of burial
must have been late Wisconsin. Inasmuch as no remains of vertebrate
animals have yet been found in Wisconsin, in the area covered by the
Illinoian drift, it is not necessary to dwell on this region. It is not
certain that there is beneath it a still older drift; but there are,
according to Alden, some indications of such deposits.
For a knowledge of the driftless area, first of all, may be consulted
the report made by Chamberlin and Salisbury in 1885 (6th Ann. Rep. U. S.
Geol. Surv., pp. 199–322, with plates). Alden’s work above referred to
maps a part of the region. Grant and Burchard have studied the geology
of the Lancaster and Mineral Point Quadrangles (Folio U. S. Geol. Surv.
145). Their text-figure 1 is here reproduced, inasmuch as it shows the
relation of the region to the surrounding glaciated areas (fig. 14). The
topographical map of Folio 145 and that of Chamberlin and Salisbury will
show the uneven character of the surface. This has resulted from the
erosion undergone during the whole of the Pleistocene. Much of the area
is covered with a coating of loess. Along Mississippi River this may be
as much as 10 feet thick, but at a distance of from 30 to 40 miles it
becomes reduced to a few inches. Considering this erosion, one might
conclude that few vertebrate remains would be preserved; nevertheless
they are not wholly missing.
In 1862 (Geol. Surv. Wisconsin, vol. I, p. 136), J. D. Whitney stated
that he had found in a crevice at Blue Mounds, Wisconsin, remains of the
mastodon (p. 111), a peccary (p. 219), bones and teeth of a buffalo (p.
270), and a wolf which he referred with doubt to _Canis latrans_. The
depth was uncertain, but it may have been as much as 40 feet. The
fossils were embedded in reddish clayey loam, the usual crevice earth.
On page 422 of the same volume, Jeffries Wyman referred the wolf remains
to two distinct species, _Canis occidentalis_ and _C. latrans_. In 1876,
Dr. J. A. Allen (Amer. Jour. Sci., ser. 3, vol. XI, pp. 47–49) described
from the same lot of bones the species _C. mississippiensis_. This
apparently did not include jaws and teeth that Wyman had referred to _C.
occidentalis_. In Wyman’s paper, on page 422, he assigned three teeth to
_Dicotyles torquatus_, an existing peccary, without stating that it had
been found at Blue Mounds. In 1869 (Jour. Acad. Nat. Sci. Phila., ser.
2, vol. VII, p. 384), Leidy referred this peccary to his _Dicotyles
lenis_, an extinct species. Inasmuch as the peccaries found at Galena
were identified by Leidy (Whitney, vol. cit., p. 424) as _Platygonus
compressus_ (p. 218), it appears pretty certain the _Dicotyles lenis_
(_Tagassu lenis_) was among the fossils collected at Blue Mounds (p.
219). It must, however, be kept in mind that Whitney, on page 35, stated
that he had collected bones and teeth of the same animal near Dubuque,
Iowa. Allen regarded the buffalo as belonging to an extinct species; but
it is really undeterminable. Accordingly there may be credited to this
locality the following species: _Tagassu lenis_, _Bison_ sp. indet.,
_Mammut americanum_, _Canis nubilus_ (_C. occidentalis_), _C.
mississippiensis_, _C. latrans_.
[Illustration:
FIG. 14.—Relation of driftless region of Wisconsin, Iowa, and Illinois
to glaciated areas. From Grant and Burchard. Unshaded area
represents driftless region.
]
In Whitney’s report, on page 133, he announced the finding of a large
quantity of bones of mastodons at Sinsinawa Mound (p. 111), but he did
not know at what depth they occurred. It seems probable that they had
been met with in one or more crevices.
It seems probable that the animals found in crevices in the lead region
of Wisconsin, Illinois, and Iowa belong approximately to one geological
stage of the Pleistocene. The following appears to include all known to
have occurred in such situations:
Megalonyx jeffersonii?.
Platygonus compressus.
Tagassu lenis.
Odocoileus virginianus?.
Cervus canadensis.
C. whitneyi.
Antilocapra americana.
Bison sp. indet.
Mammut americanum.
Marmota monax.
Microtus sp. indet.
Geomys bursarius.
Sylvilagus floridanus? (Lepus sylvaticus).
Anomodon snyderi.
Procyon priscus.
Canis nubilus (C. occidentalis).
C. mississippiensis.
C. latrans.
The writer was at one time inclined to believe that these animals
belonged to the time succeeding the withdrawal of the Wisconsin
ice-sheet. Baker (“Life of the Pleistocene,” p. 353) thinks that they
belong probably to the Peorian, inasmuch as the region is covered by
Iowan loess, beneath which many of the bones have been found. It is
quite probable that those crevices were open during at least some part
of the Pleistocene and that animal remains collected in them. The
fossils are reported as being sometimes inclosed in a matrix of cave or
fissure materials which are cemented together by iron. The considerable
number of extinct species, certainly 7 out of about 18, makes it
probable that the fauna is not so recent as the Late Wisconsin.
It appears to be determined that the Iowan loess was formed immediately
after the retirement of the Iowan ice-sheet. It might, therefore, be a
question whether all of these animals might have got into those crevices
in time to be covered in by the loess. On the other hand, the Illinoian
drift was, for a long time, exposed to weathering and erosion before the
Iowan drift and loess were laid down. Also, the Sangamon interval was
probably much longer than the Peorian, so that the chances for the
accumulation of the fossils were greater. It seems, however, that we can
only say that the fossils are post-Illinoian and probably pre-Wisconsin.
Besides the vertebrate fossils referred to above, a few others,
especially mastodons (pp. 110, 111), have been found at other places,
but so little is known of the conditions of their interment that they
furnish little geological information.
A very interesting region is found in the western part of the State, in
Dunn and Pepin Counties. This has been examined with great care by Dr.
Samuel Weidman, State geologist of Wisconsin. About Menomonie there are
several brickyards, whose excavations furnish opportunities for studying
the formations at that point. Sections of one of these brickyards are
described and illustrated by Dr. E. R. Buckley, in Bulletin VII, part 1
(1901), page 194, plate XXXVII. A section and brief description is found
also in a paper by Dr. Hussakof (Jour. Geol., vol. XXIV, p. 688). In
that region are found outwash gravels which have been definitely
correlated by Weidman with Iowan drift. In some places this is overlain
by loess. These gravels vary from 10 to 20 feet in thickness at
Menomonie. Beneath the gravels are found lacustrine clays varying in
thickness from 20 to 40 and even 60 feet. These are stratified and
consist of layers from 1 to 12 inches in thickness, with intervening
thin layers of sand. Toward the bottom the sand increases in amount.
Beneath the clay-bearing formation is a bed of sand attaining a maximum
thickness of about 150 feet. This is underlain by coarse sand and
gravel. The lacustrine clays and the underlying sands and gravels are
included by Weidman in his Menomonie formation, and this is believed by
him to be of Sangamon interglacial age. In northwestern Wisconsin are
found other glacial deposits believed to belong to the Illinoian drift
epoch.
In the lacustrine clay at Menomonie have been found remains of the great
lake trout, _Cristivomer namaycush_ (Hussakof, as cited above), of a
deer (p. 230), a caribou (p. 247), and probably a mastodon. The deer is
represented by a single vertebra, identified by Dr. W. D. Matthew. The
supposed mastodon is indicated by the distal end of the right femur, the
caribou by an antler of a young and probably female individual and by
the shaft of a large individual.
At Woodville, in St. Croix County, about 20 miles west of Menomonie, has
been found a forest bed regarded as belonging to the Aftonian. This was
described by Arthur Koehler (Amer. Forestry, vol. XXVI, Feb. 1916, p.
92, 3 figs.). Wood was found that was identified as that of spruce.
In 1913 (Science, n. s., vol. XXXVII, p. 457), in a brief abstract,
Weidman reported that in Wisconsin he recognized drift deposits of
Wisconsin, Iowan, and Kansan ages and another still older. No localities
were mentioned, but his statements were doubtless based mostly on his
work in the western part of the State. The loess was found to be laid
down after the Iowan and before the Wisconsin. Interglacial deposits
were found between the Kansan and the Iowan.
In 1905 (Jour. Geol., vol. VIII, pp. 238–256) and in 1910 (Jour. Geol.
vol. XVIII, pp. 542–548), Dr. R. L. Chamberlain presented the results of
his investigations on the “Pleistocene Geology of the St. Croix Region
in Western Wisconsin.” His conclusion (p. 548) was that in that part of
the State there were present (1) a surface mantle of gray Wisconsin
drift deposited by a glacier from the Keewatin center; (2) red Wisconsin
drift deposited by a glacier coming from the Labrador center; (3) a red
drift left by an ice invasion from the Labrador center, its age
consistent with Illinoian; (4) a grayish-black till that had come from
the Keewatin center and whose age was probably Kansan.
MARYLAND AND DISTRICT OF COLUMBIA.
For obvious reasons the Pleistocene geology of the District of Columbia
is considered in connection with that of Maryland. This region is of
especial interest, because of the long time and the care which has been
bestowed on it by geologists and because the conclusions reached have
been applied to the geological study of States both toward the north and
toward the south.
The most complete exposition of the Pleistocene geology of the region is
to be found in the volume of the Maryland Geological Survey entitled
“Pliocene and Pleistocene,” published in 1906. The geological treatise
itself was written by George Burbank Shattuck and is illustrated by many
maps and text-figures. Included in this is a bibliography of the subject
which occupies 17 pages. There is a chapter by W. B. Clark, Arthur
Hollick, and F. A. Lucas, on the interpretation of the palæontological
criteria; another by F. A. Lucas on the mastodons and the elephants. The
Pleistocene mollusks found in the State, 40 species, were described and
figured by W. B. Clark; while the plants, also nearly 40 in number, were
described and figured by Arthur Hollick.
The history of the development of our present knowledge of the geology
of Maryland and the classification of its formations up to 1906 is given
by Shattuck in the volume just cited (pp. 25–40). This geologist
recognized in the superficial deposits of the State five formations
(fig. 15). These are, beginning with the oldest, Lafayette, Sunderland,
Wicomico, Talbot, and Recent.
[Illustration:
FIG. 15.—Diagram showing the ideal arrangement of the supposed
terraces in the Maryland Coastal Plain. From Shattuck.
]
The Lafayette is regarded as having been laid down during the Pliocene.
The Sunderland, Wicomico, and Talbot form three terraces, of which the
Sunderland is the oldest, most elevated, and farthest away from the
larger bodies of water. It is composed of clay, peat, gravel, and
boulders supposed to have been brought in by the ice. The coarser
materials appear to occupy usually the lower parts of the formation. The
elevation near Washington is about 200 feet, but southward it descends
gently, until in St. Mary’s County it is only about 60 feet. The
thickness varies from about 80 feet to nothing. According to Shattuck,
at the time of deposition of the Sunderland the coast was depressed to
an extent of about 200 feet, so that its materials were laid down either
in salt water or in that of wide estuaries. No deposits belonging to it
have been found in the eastern peninsula. In the western peninsula
considerable areas are recognized along the Potomac up to Washington and
along the Patuxent and Chesapeake Bay to Baltimore and Elkton. Except in
the southern part of this peninsula, the Sunderland is found only in
widely separated patches. No marine organisms are known to have left
their remains in the Sunderland, but forest trees of a number of
existing genera and several extinct species have been described by
Hollick in the volume cited.
The Wicomico formation is described as occupying a large portion of the
central and higher parts of the eastern peninsula; in the western it
forms a narrow and often interrupted fringe around the Sunderland. North
of Washington and Annapolis it occurs only in patches. Its materials are
very similar to those of the Sunderland. Its greatest elevation is about
100 feet above sea-level, and this, according to Shattuck’s view, marks
the amount of depression of the land at that time. The thickness may be
as much as 70 feet, but is usually much less. No marine fossils proper
to the period have been discovered in the deposits, but at a point in
Prince George’s County plant remains have been found in a deposit about
20 feet thick.
The Talbot formation forms a fringe, sometimes of great width, sometimes
narrow or interrupted, along all the large bodies of water in this State
and in Delaware. It is the lowest of the terraces. The greatest
elevation is about 45 feet; the thickness does not exceed 40 feet. The
materials noted are those of the other two formations—clay, peat, sand,
gravel, and ice-borne boulders. At several points along Chesapeake Bay
and on the lower part of Patuxent and Potomac rivers, deposits
containing plant remains have been discovered, including pines, cypress,
hickory, beech, elm, and black locust. In contrast with the other
formations, the Talbot has furnished many marine fossils, mostly
mollusks; but in all cases the localities are close to the present
coast.
The writer does not accept the theory that the materials forming what
have been called the Sunderland, Wicomico, and Talbot terraces have been
to any great extent laid down in the sea. Some part of the Talbot, that
lying near the present coast, has undoubtedly had such an origin. Nor
has the Coastal Plain suffered, so far as is determinable, any such
amount of depression as the theory mentioned requires. The materials of
the Sunderland and Wicomico have, in the writer’s opinion, been brought
down by rivers whose beds lay at levels nearly as high as those of the
real or supposed terraces. When the Talbot materials were laid down, the
rivers and estuaries of the coast had been cut down nearly to their
present levels, and this was not long after the beginning of the
Pleistocene.
The authors of the submergence theory admit that no satisfactory
evidence of the presence of marine organisms, vertebrate or
invertebrate, are to be found in the body of the assumed terraces,
except again in parts of the Talbot which immediately border the ocean
or the great estuaries. It is almost inconceivable that the ocean could
occupy the Coastal Plain from New Jersey to Mexico for thousands of
years and lay down great thicknesses of clay, sand, and gravel without
having left somewhere beds of molluscan shells in such situations that
they would have been discovered. While these marine fossils are lacking,
there are found on all these terraces from Maryland to Florida and to
the Rio Grande an abundance of land vertebrates such as elephants,
mastodons, horses, camels, peccaries, and many other forms. Nor do our
palæobotanists have difficulty in finding oaks, walnuts, hickories,
poplars, etc. On the theory of submergence there are missing all the
things that ought to be found and there are met with just the things
that would not be expected.
A figure is here reproduced (fig. 15) from the Maryland Pliocene and
Pleistocene volume, page 66, with the explanation there accompanying it.
The reader may judge for himself whether the sea could occupy the
Atlantic coast since Pliocene times without leaving any traces of marine
fossils, while at the same time there were preserved in those terraces
remains of land animals and land vegetation.
Another section (fig. 16) is reproduced from Folio 179 of the U. S.
Geological Survey, the authors of which are G. W. Stose and C. K.
Swartz. The uppermost terraces are by these authors supposed to belong
to the late Pliocene, the formation formerly known as the Lafayette.
These figures suggest that the one set of terraces have some connections
with the other set.
[Illustration: