
AGE OF THE LIGNITE FORMATION. 197 
ae 
founded on our ignorance, or local knowledge, and had the recognised 
elassification of formations been based on a study of the western interior 
region of North America, it is probable that there would have been no 
on line drawn between Mesozoic, and Tertiary or Cainozoic ; or had there 
h been, it would be placed altogether above the Lignite series, which 
represents, at least in part, the lower Tertiaries of other countries. This 
at least would have been the grand classification founded on great areas, 
and not invalidated by the existence in a few places,—as probably at 
_ Evanston,—of beds of transition upward. If, however, it is desirable 
to draw a line between Cretaceous and Tertiary for the sake of uniform- 
-ity with other and better known regions, and for use as a boundary in 
geological mapping ; no physical non-conformity offering, it becomes 
necessary {o turn to the included organic remains, which might indicate 
the position of some gap otherwise concealed. These we have seen, 
however, do not offer evidence of a very certain tenor; but from it, such 
as it is, our conclusions must be drawn. 
454. The plants and fresh-water molluscs do not appear to be capa- 
ble of rendering much service. The flora of the Dakota group,—the low- 
est of the Cretaceous of this region, and the probable equivalent of the 
lower or grey chalk of Europe—is well represented in some localities, 
but is so essentially modern in type, that it was by competent authorities 
referred to the Miocene period. The distinctive facies of the flora of 
America, seems even then to have been sketched out ; and from this early 
period to the present day, wherever a land surface presented itself, plants 
very similar in appearance, and differing for the most part only specifi- 
cally, were ready to occupy it. No great wave of vegetation of Indian 
and Australian type, like that characteristic of the typical Eocene of 
Europe, seems to have swept over this continent, and thus the plants of 
the American rocks are not strictly comparable with those of the old 
world. They belong to a separate region, the features of which are its 
own, and must be worked out by themselves. 
455. Yet further doubt, however, rests upon the evidence of the 
plants; for Prof. Lesquereux, from a careful comparison of the flora of 
different localities of the newer formations of the interior and western 
regions, is led to a sub-division and arrangement in series of the beds of 
these places, which is in many instances manifestly untenable in the 
face of other evidence. This is especially the case when he includes the 
Placiére coal beds ot New Mexico, and the Nanaimo coals of Vancouver 
Island, from palsophytological reasoning, in the Lower Eocene, The 


