Otto E. (Otto Emery) Jennings.

Fossil plants from the beds of volcanic ash near Missoula, western Montana (Volume vol. 8 no. 2) online

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Vol. VIII. No. 2.


By 0. E. Jennings.



This paper deals with some fossil plants obtained by Mr. Earl Douglass from
the beds of volcanic ash in the vicinity of Missoula, Montana, and with a smaller
collection made by him near Winston, Montana. The specimens are now in the
Carnegie Museum.

The fossils from near Missoula were collected bj' Mr. Douglass from two' places.
One of these places is termed on the labels "Locality 165" and is stated to be about
one and one-half miles north of Missoula, the collections having been made Sep-
tember 26-30', 1903. These beds are noted as being "Several hundred feet thick
and are composed of volcanic ash, sandstone, conglomerate, etc. There are several
seams of coal." Another label from the same place says: "In beds of volcanic
ash. Coal above and below." The other station from near Missoula, and from
which the better part of the material came, is evidently near "Locality 165" and is
called on the labels "Locality 196." The collection from Winston was made on
September 23, 1902, on the north side of Beaver Creek, northeast of Winston,
Montana. This latter collection is a small one, containing but two or possibly
three species.

The Missoula collections, with which this paper is mainly concerned, were



taken by Douglass from beds which he beheved to be of Ohgocene age.^ He states
that they "appear in the main to represent the Titanotherium and Oreodon beds
of South Dakota." This horizon, as understood by most American paleontologists,
includes approximately the lower half of the White River formation.^ The
fossil plants in these deposits consist of impressions of leaves and of leafy twigs,
there being also a few impressions of fruits and leafless twigs. The Missoula
specimens are in a very light colored, grayish-white, soft and friable rock, consisting
of a fine-grained volcanic ash, which was evidently more or less stratified and lami-
nated.'-* It is generally believed that the dust was wind-borne and that it was
mainly deposited in freshwater lakes or other shallow basins. Douglass states
that "It does not appear that the water was as a rule very deep. There are un-
doubtedly not only lake but marsh and river deposits. . . . We find nearly every-
where evidences of shallow water, such as ripple marks, bird tracks, plant remains,
shallow water mollusca, etc." Rowe*^ also states his belief that the ash fell in
freshwater lakes.

The Missoula specimens mostly preserve in considerable detail even the finer
venation of the leaf surfaces, and in a number of instances the outline of the whole
leaf is plainly evident. The Winston specimens are, however, in a harder, light
gray rock, which has slickenside surfaces developed at various angles and directions
and presents every appearance of having once been a slumping mass of very fine-
grained mud. In this material the fossils are unsatisfactory, the hardness of the
rock and its irregularity of fracture resulting in fragmentary specimens.

I have undertaken the study of these various collections more as a student of
modern systematic botany and ecology than as a paleobotanist, and it is barely
possible that my conclusions may in some instances differ from what might have
been those of a paleobotanist, trained as a stratigrapher. However, no sharp line
of distinction can now be drawn between the work of a paleobotanist on the one
hand and that of the student of modern botanj'- and ecology on the other, and it is
plainly evident that each of these fields of study may j^et receive many valuable
and enlightening contributions from the other.

In the preparation of the illustrations accompanying this article I have had
the able assistance of my wife, Grace K. Jennings, and to her is due quite largely

■ Douglass, Earl. New Vertebrates from the Montana Territory. Annals Carnegie Museum, II,
1903, 145-199.

^ Willis, Bailey. Index to the Stratigraphy of North America. TJ. S. Geol. Surv., Prof. Paper
LXXI, 1912, p. 770.

=* Rowe, J. P. Some Volcanic Ash Beds of Montana. Univ. Montana Bull., XVII, 1903.

" Op. cit., p. 146.

^ Op. cit., p. 12.


the excellence of manj'^ of the photographic reproductions. The photographs were
made with an ordinary 5 X 7-inch bellows camera, the specimens being usually
placed in direct sunlight at a low angle of incidence in order to give sharper contrast
and to show better the features of relief on the impressions. The photographs
showing parts of the specimens enlarged were made by supplementing the ordinary
lens of the camera with an enlarging lens which fits over the front of the regular
lens like a cap. To give greater contrast in these enlargements ordinary daylight
was supplemeated with a rather strong desk dissecting lamp fitted with "daylight"
glass and by proper manipulation of this light the inequalities on the surface of the
leaf impressions were shown as highlight and shadow.

In the publication just referred to Rowe gives a short list of the plants collected
from beds of volcanic ash near Missoula, the list being as follows:

1. Sequoia Langsdorfii. 6. Cornus or Viburnum.

2. Sequoia, probably new species. 7. Populus balsamoides (?)

3. Glyptostrobus europceus. 8. Fruit near Chinchonidium.

4. Alnus. 9. Taxodium occidentalis.

5. Carpinus, probably new species. 10. Taxodium.

Accompanying Rowe's report are three plates illustrating some of the fossil
plants from these beds. Plants shown on these plates are evidently the same as
some of those described in the present paper, as follows: Plate VI shows at the
left upper margin what is probably a piece of a leaf of Alnus Hollandiana Jennings,
a specimen of Populus Zaddachi Heer being shown in the middle of the plate,
while both Plates VI and VII show leaves of what I have described as a new species,
Betula multinervis. The Taxodium-\ike sprays in Plate VIII are evidently the same
as the sprays in our material which I believe to represent one of the various types of
Sequoia Haydenii (Lesquereux) Cockerell.

The Glyptostrobus mentioned in Rowe's list is probably the same as the speci-
mens in our collections which I believe belong to Sequoia Haydenii. The Carpinus
is evidently the same as my Betula multinervis; the Populus balsamoides (?) I take
to be Populus Zaddachi Heer and the Taxodium, like that shown in his Plate VIII,
at least, is probably Sequoia Haydenii.

II. Relations of the Fossil Flora from Missoula to the Nearest Eocene
AND Miocene Floras of the West.

The specimens collected by Mr. Douglass from near Winston appear to repre-
sent but two, or possibly three, species, as follows :


Equisetum insculptutn Jennings
Equisetum sp. Vegetative buds
Aralia longipetiolata Jennings

These species appear not to be represented in collections described from other
localities and this fact, in connection with the wide geological ranges of the genera
Equisetum and Aralia, makes the collection of little value as a means of correlating
this flora with other ancient floras.

The specimens from the Missoula district represent at least twenty species,
ten of which I have described as new and one of which requires a new name. These
twenty-one species are enumerated in the following list, the numbers in parentheses
indicating from which of Douglass' localities the specimens came :

Sequoia Haydenii (Lesquereux) CockereU. (165, 196)

Sequoia oblongifolia Jennings. (196)

Thuy apsis gracilis Heer. (196)

Sabina lingucefolia (Lesquereux) CockereU. (196)

Typha Lesquereuxii CockereU. (196)

Cyperacites sp. (196)

Populus smilacifolia Newberry. (165)

Populus Zaddachi Heer. (165, 196)

Juglans pentagona Jennings. (165)

Betula multinervis Jennings. (165, 196)

Alnus microdontoides Jennings. (165, 196)

Alnus Hollandiana Jennings. (196)

Quercus approximata Jennings. (196)

Quercus fiexuosa 'Newberry. (165)

Quercus laurisimulans Jennings. (196)

Ficus (?) prunifolia Jennings. (196)

Ilex furcinervis Jennings. (196)

Celastrus parvifolius Jennings. (196)

Acer oregonianum Knowlton. (165)

Vaccinium palmocorymbosum Jennings. (196)

The flora represented in the Missoula collections appears closely related to
that reported for the Florissant basin of Colorado." Of the fifteen genera repre-

* Among the more important titles consulted with reference to the Florissant flora were the following:
Kirchner. Trans. St. Louis Acad. Sci., VIII, 1S98, pp. 161-198, Pis. 11-15.
CockereU. Univ. Colorado Studies, III, No. 3, 1906, 1.57-176. Bull. Am. Mus. Nat. Hist.,

XXIV, 1908, pp. 71-110, Pis. 6-10. Amer. Nat., XLIV, 1910, pp. 31-47.
Knowlton. Proc. U. S. Nat. Mus., LI, 1916, pp . 241-297, Pis. 12-27.


sented in the Missoula flora all but two are also represented in the Florissant.
Three species, Sequoia Haydenii, Typha Lesquereuxii, and Sabina lingucefolia,
apparently occur in both floras and there are other species which a further study of
more complete and more abundant material might prove to be identical. Further
comparisons show that to a large extent the genera having more than one species
each in the two floras were largely the same. In the Missoula flora Sequoia,
Populus, Alnus, and Quercus were each represented by more than one species..

One of the fossils in the Missoula collection apparently represents the species
described by Knowlton from the Mascall beds of the John Day Basin, Oregon, and
in a number of respects the Missoula flora seems to be rather closely allied to the
Mascall flora. Eleven of the Missoula genera occur in the Mascall and, while,
with the exception of the maple, perhaps none of the corresponding forms in the
two floras are identical, some of them are rather closely similar. Of the genera
reported as having two or more species each, the Mascall flora has Sequoia (with
2 or 3), Quercus (5 or 6), Celastrus (2), and Acer (8), as against Sequoia (2), Populus
(2), Alnus (2), and Quercus (3) in the fossil flora at Missoula.

Another of the floras of the John Day Basin reported by Knowlton^ aad of
interest with reference to the Missoula collections is that from what are regarded as
upper Eocene^ beds at Bridge Creek, Oregon. Comparing the Missoula flora with
that of Bridge Creek it aiDpears that seven of the fifteen genera of the former are
represented also in the latter. Of the genera of the Bridge Creek flora represented
by more than one species there are Sequoia (with 2 species), Juglans (3), Betula (4),
Alnus (4), Quercus (8), Ficus (1), Acer (1). The Missoula flora has Sequoia (2),
Populus (2), Alnus (2), and Quercus (3), so that, considering the relative percentage
of species represented by the leading genera together with the number of genera
common to the two floras, it would appear that the flora from Missoula is about as
closely related to the Bridge Creek flora as to that of the Mascall beds.

Knowlton" has reported eighteen genera of plants among the fossils collected
in the Payette formation (regarded by Knowlton as Upper Eocene)^" from the

' Knowlton. Fossil Flora of the John Day Basin. U. S. Geol. Surv. Bull., CCIV, 1902, pp. 19,
89-93, 106-108, 113. Op. cit, pp. 17, 89-93, 103-105, 113.

* Merriam, J. C. Significant Features in the History of Life on the Pacific Coast, in Nature and
Science on the Pacific Coast, 1915, pp. 88-103. See also A Contribution to the Geology of the John Day
Basin. Bull. Dept. Geol., Univ. Cal., II, 1901, 269-314, 285-287, 290-299; also Merriam, J. C, and
Sinclair, W. J. Tertiary Faunas of the John Day Basin. Bull. Dept. Geol, Univ. Cal., V, 1907, p. 173.

s Knowlton. The Fossil Plants of the Payette Formation. U. S. Geol. Surv. Ann. Rpt., XVIII,
Part III, 1898, pp. 721-736, Pis. 99-102.

'° Knowlton. Succession and Range of Mesozoic and Tertiary Floras, in Willis and Salisbury,
Outlines of Geologic History, Chapter X, 1910, pp. 200-211.



fossil lake beds of the Snake River in western Idaho. Eight of these genera are
common to the Payette and Missoula collections. Of the Payette genera five are
represented by more than one species each (Sequoia, Myrica, Populus, Betula, and
Quercus) as against fom' such genera in the Missoula collections (Sequoia, Populus,
Alnus, and Quercus). While not identical in the two floras a number of species
are here also represented by similar forms.

The Lamar flora described by Knowlton^^ from the Yellowstone National Park
has listed for its lower member ("Fossil forest a") eight of the fifteen genera which
I have recognized in the Missoula collections, and there are at least five or six
species closely similar in these two floras.

From what he regards as the true Green River formation "excluding Florissant
and Elko Station," CockerelP^ has compiled a fist of the plant genera represented.
A comparison of this list with the list of Missoula genera shows nine genera to be
common to the two floras.

The following table presents in a more compact form a list of the plant genera
represented in the Missoula collections together with the occurrences of the genera
in the other floras discussed in the preceding pages :

Table of the Genera Represented in the Collections of Fossil Plants from the Beds of Vol-
canic Ash near Missoula, Montana, showing also the Occurrence of these Genera in a
Number of other Fossil Floras.

Regarded as Upper Eocene.

Middle Miocene.

White River.
Missoula, Mont.



National Park.

Green River.

Wyoming and


Snake River,
West Idaho.

Bridge Creek.




Thuijopsis. . . .



Cyperacites . . .



































Vaccinium . . .


" Knowlton. Fossil Flora of the Yellowstone National Park. U. S. Geol. Surv., Monograph
XXXII, Part II, Chapter XIV, 1899, pp. 651-791.

i^Cockerell. The Fossil Flora of Florissant, Colorado. Bull. Amer. Mus. Nat. Hist., XXIV,
1908, p. 44.


It is obviously unsafe in questions of comparison or correlation between,
rather closely related floras to place much reliance on such evidence as may be
furnished by a small collection of fossil plants consisting mainly of leaf -impressions.
Conditions of deposition and fossihzation are probably very rarely effective in
preserving a representative sample of a flora, unless the fossils collected are in
large numbers. As far as the indications go, it appears that the Missoula specimens
represent much the same kind of a flora as was preserved in the Florissant beds.
Yet differences between the Missoula flora and the Green River flora, as referred to
above, and generally regarded as Upper Eocene^^ in age, is by no means great.
The Florissant beds are now regarded as Miocene^*, Cockerell even advancing both
the Mascall and Florissant floras to middle Miocene. ^^

As far as the genera are concerned collectively there has been comparatively
little change in the flora of the temperate regions of the United States since Floris-
sant times, and, allowing for a probably gradual cooling and a decrease in moisture
during the period between the Green River (Eocene) and the Florissant (Middle
Miocene), it appears that the changes in genera in this latter period were Ukewise
not great. Cockerell, comparing the Intermediate and Lamar floras on the one
hand and the plants "said to occur elsewhere or in the Eocene" on the other, shows
that these Yellowstone floras have "twenty-six plants specifically identical with
those of the basal Eocene" and, further, "The conclusion seems to be legitimate
that the Yellowstone Intermediate and Lamar florse are Upper Eocene, or at least
older than Miocene." In his discussion of the records furnished by fossils as to
the distribution of the various floras through the different periods of time,. Clements
says^'' that " the flora of the Oligocene was essentially that of the Eocene somewhat
reduced by deformation, and the plants of the Pliocene are practically those of the
Miocene, but with a striking reduction," the reduction mentioned being due in
part to the reduction in the area in which sedimentation and fossihzation were
taking place.

Of the floras referred to in the above discussion and in the table, the Bridge
Creek, Lamar, Payette, and Green River are now probably best regarded as late

" Willis. Index to the Stratigraphy of North America. U. S. Geol. Surv., Prof. Paper LXXI,
1912, pp. 676, 758-760, 765.

" Knowlton. A Review of the Fossil Plants in the United States National Museum from the
Florissant Lake Beds of Florissant, Colorado, With Descriptions of New Species and Lists of Type
Specimens. Proc. U. S. Nat. Mus., LI, 1916, pp. 241-297, Pis. 12-27.

'=■ Cockerell. The Miocene Trees of the Rocky Mountains. Am. Nat., XLIV, 1910, pp. 31-47;
Some American Fossil Insects. Proc. U. S. Nat. Mus., LI, 1916, pp. 81-106.

" Clements, F. E. Plant Succession. Carnegie Inst. Wash., Publ. CCXLII, 1916, p. 352.


.Eocene, the Mascall and Florissant as middle Miocene. Assuming this to be the
case it is interesting to group together the four upper Eocene floras for purposes
of comparison with the two Miocene floras. Upon doing this it appears that of
the fifteen genera in our Missoula flora twelve occur also in the combined upper
Eocene floras and fourteen in the combined middle Miocene floras. This compari-
son does not show any great preponderance in favor of the Miocene, and it is
quite possible that climatic and other ecological conditions may have brought
about similar groupings in the Missoula and Florissant floras somewhat out of
proportion to the actual systematic relationships of the floras existing at the time
these fossils were formed.

The Missoula flora probably occupied the shores and surrounding slopes of a
high mountain lake. Douglass says, however: "There is doubt that the mountains
were as high during the White River epoch as at the present time."" Cockerell
and other writers have referred to Lake Florissant as a mountain lake and some of
the differences between the Mascall and Florissant floras are thought by Cockerell
to be possibly due to the differences between a lowland flora, like that of the MascaU,
and one around a mountain lake, such as that of the Florissant.^* I am inclined
to believe that the similarity of habitat has brought about a similarity in the fossil
floras from Missoula and Florissant that may have obscured to a considerable degree
the actual difference of the two floras in point of time.

Two of the plants represented in the Missoula collections {Thuyopsis gracilis
Heer, and Populus Zaddachi Heer) appear to be the species described and reported
by Heer from the Atane beds of Greenland. These beds were regarded by Heer^^
and some other authors-" as Miocene, but they are more likely Cretaceous or early
Eocene.-^-" A considerable number of plants described from the arctic regions by
Heer and others from beds thought at that time to be Miocene appear farther south
during early and middle Tertiary times. This southward shifting of floral zones is
to be ascribed to corresponding climatic changes. Clements notes-^ that 'A
distinct cooling is indicated by the flora of the early Eocene, and the usual accom-

'' Douglass. New Vertebrates from the Montana Territory. Annals Carnegie Museum, II,
1903, p. 149.

1* Cockerell. The Miocene Trees of the Rocky Mountains. Am. Nat., XLIV, 1910, p. 37.

'" Heer, 0. Flora Fossilis Arctica I, 1S6S, pp. 98-99, and various other pages in this and other
volumes of the series.

-" Schuchert, C. Climates of Geologic Time. In Huntington's The Climatic Factor. Carnegie
Inst. Wash., Publ. CXCII, 265. 1914.

21 Willis, Bailey. Index to the Stratigraphy of North America. U. S. Geol. Surv., Prof. Paper
LXXI, 1912, pp. 705 and 838.

'- Clements, F. E. Plant Succession. Carnegie Inst. Wash., Publ. CCXLII, 1916, p. 242.


paniment of aridity is shown by the salt and gypsum beds of the Texas formations
of the period. The earliest Eocene flora, that described by Heer from Belgium,
indicates a temperate climate, characterized by Quercus, Castanea, Salix, Laurus,
Hedera, etc. Similar horizons are found in the lower Eocene of France and England.
At a later stage, palms, bananas, figs, cinnamons, etc., became dominant, indicating
a return to tropical conditions.' With the period of "mountain making and vul-
canism" in the Oligocene there came another change to a cooler and drier climate. ^^
Clements further notes-'* that the evidence indicates "that the Oligo-Miocene cycle
was marked by a general chmate cooler and drier than that of the Eocene, and hence
by a differentiation of chmates approaching that of today. " And, further, " So far as
dominants are concerned there appears to be little difference between the floras of
the Eocene and Miocene. The dominant tree genera appear to have been about
equally represented in both, and this is largely true of shrubs. . . . Thus, while
the flora remained largely the same, it must have undergone marked differentiation
and shifting as a result of the deformation and cooling which initiated the cycle.
The northerly climax zones must have been broadened as well as pushed to the
south. . . . Before the chmatic effect of Oligocene deformation had disappeared
the deformation cycle of late Miocene and Pliocene had begun to culminate in the
Ice Age. Thus the shifting of the climatic zones took place only to the southward,
as well as downwards on the mountains." The cooling during the Oligo-Miocene
cycle "from a tropical or subtropical climate to a warm temperate one over much of
the continent was permanent."

Assuming, then, that during the period from the late Eocene up into the
Miocene there was, in general, a cooling and drying of the climate and a differentia-
tion of climatic regions and zones and, further, that during this time there was a
migration of northern plants southwards as well as down from the higher and
cooler habitats to the lowlands, it seems to me not unreasonable to beheve that the
mountains of western Montana during the Oligocene would have been populated by
the northern flora long before a similar region in central Colorado at a latitude of
about six hundred miles farther south. The Missoula region would likely have
been invaded by this northern flora long before the Mascall region Ijdng to the
southwest in Oregon and probably on lowlands separated but little from the western
ocean either by distance or elevation. Unless exception might be made in the case
of the Payette flora, I feel fairly certain that the Florissant was the only one of the
fossil floras discussed which approximated very closely the Missoula flora as to the

^' Schuchert. Op. cit.

-' Clements. Op. cit, pp. 364-366.


ecological conditions involved. I think that the similarity of the Missoula and
Florissant floras may actually be regarded as indicating a considerable time interval
during which similar stages in a southward migration of northern plants were
reached in the two floras. During the corresponding disappearance of the southern
plants the Missoula region would, of course, lose them before they would disappear
from the Florissant and, in this connection it is interesting to note that of the
southern element Florissant had Sapindus, Diospyros, Persea, Leuccena, Annona,
Ficus, and others, while only one such species, which I doubtfully determined as
Ficus, appears in the Missoula collection. All this leads me to believe that the
collections from Missoula represent an earlier period than do the Florissant collec-
tions, a period somewhere between the late Eocene and middle Miocene, and T
see no reasons for not accepting Douglass' claim that the beds belong to the White
River formation and are of Oligocene age.

If we may accept the claim that there had come about a differentiatioQ of
climates it would not be unreasonable to expect a considerable difference between

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