9? >) 3 "ee 
328 B. N. A. BOUNDARY COMMISSION. 

In my judgment, any precise decision as to their geological age is premature. 
We have before us the fact that at a time when the Cretaceous fauna still prevailed 
in the sea, the land plants of America had already come in under the existing generic 
forms, and that some modern species had been introduced, and in the intervening 
time, while very decided changes have taken place in animal life, this flora has per- 
sisted with only specific change, and with no marked breaks. At the same time, it is 
evident that local diversities of station were sufficient to produce very distinct floras 
in different localities at one and the same time, and the paleontological botanist is. 
constantly in danger of mistaking local diversities for differences in age, and on the 
other hand, if correlating beds of different ages, in consequence of the similarity of 
their fossils. 
In these circumstances, it is rash to identify the beds, on the evidence of plants 
alone, with particular sub-divisions of the Tertiary elsewhere. In order to do this 
with certainty, it will be necessary to wait until the stratigraphical relations of the 
beds are better understood, and until sufficiently extensive collections haye been 
made to enable us to eliminate local differences, and to understand the actual pro- 
gress of the changes on the great scale which have occurred between the Cretaceous 
‘period and the present time. In the meantime, it is sufficient to hold that we have 
here a flora which in Europe would be regarded as Miocene, but which in America 
probably began to exist at a much earlier date, 
The small collection of plants from a dark clay, at Great Valley, indicates a 
somewhat different assemblage of species from that of the other localities, though 
believed to be on the same geological horizon. The leaves are mostly fragmentary, 
and not so well preserved as those of Porcupine Creek. Among them are Conifers 
referable to Sequoia Langsdorfii and Glyptostrobus Europxus, a Populus with large 
round cordate leaf, having distinct obtuse teeth, and pinnate venation, and resembling 
P. grandidentatus, a Sapindus, perhaps S. afinis of Newberry, a Cinnamomum, one or 
more narrow-leaved species of Quercus, a leaf similar to Hedera McClureit of Heer, 
and the remarkable equisetaceous plant described below, Physagenia Parlatorii, Heer 
Such an assemblage, supposing it to be on the same geological horizon, may be 
accounted for by supposing a marked difference of station, or some local change of 
vegetation, depending, for example, on an extensive forest fire, or perhaps the afflu- 
ence of a river bringing vegetable material from a distance. The flora as a whole 
has perhaps more resemblance to that of Lesquereux’s fourth or Green River group, 
as mentioned in Hayden’s report of 1873. 
The following list of species includes all the forms which I can certainly identify 
with the aid of the present material. In determining several of the species, and in 
comparing them with those found in the United States, I have been much aided by 
the kindness of Prof. Newberry. 
Filices. 
OnocLeA sensrpitis, L.—This well-known modern Fern, which occurs also in the 
Miocene of the Isle of Mull, in Scotland, and in the Fort Union group of Dakota, is 
found in great abundance in the clays at Porcupine Creek. Dr. Newberry has shown 
that it is not distinguishable from the existing forms, but most resembles that known 
as var. obtusiloba of Torrey. 
