

AGE OF THE LIGNITE FORMATION. 195 
sandstone,” which is regarded as the lower bed of the Tertiary.* 
ep Though the Cretaceous subdivisions are not well defined in the Southern 
Rocky Mountain region, so much so that it has been said by Hayden, 
that “ if they had first been studied along the base of the mountains only 
from Cheyenne southward, it is very doubtful whether the five distinct 
groups of strata would have been made out,’ yet, even where the lines 
; are thus indefinite No. 5 is clearly represented, and holds the same 
ee relations to the underlying and overlying series that it does on the forty- 
. ninth parallel. The black shales of No. 4 are said to “ pass gradually up 
_ into yellow rusty arenaceous clays which characterize No. 5, and No.5 
passes up into the Lignite Tertiary beds where they can be seen in 
contact, without any well defined line of separation that I could ever 
discover’ + In other localities Dr. Hayden has denominated arenaceous 
layers which seem to occupy the same horizon, “ transition beds.” He 
writes “In various portions of the Laramie Plains, Colorado, Raton 
Hills, &. I have observed between the well defined Cretaceous and 
Tertiary beds, a group of strata composed of thin layers of clay with 
yellow and grey sands and sandstones, which I have called transition 
or beds of passage.” “ There is no proof so far as I have observed in all 
the Western country of non-conformity between the Cretaceous and 
Lower Tertiary beds.”{ Examples might be multiplied, but sufficient 
have been given to illustrate the nature of the junction, and its similarity 
over the broad area explored by the U.S. geologists, and on the forty- 
ninth parallel and northward. 
450. The perfect stratigraphical continuity of the Upper Cretaceous 
and Lignite formation is apparent everywhere. No break occurs from the 
base of No. 4, up-through that division and No. 5, onward through the 
whole thickness of the beds associated with the lignites. The period of 
; the deposition of the Lignite formation, is however, almost everywhere, 
‘ brought definitely to a close by the occurrence of a mountain-making era, 
4 during which a great part of the Rocky Mountains was elevated, and the 
4 succeeding Tertiary beds, when they occur, are frequently found to rest un- 
4 | conformably on the Lignite strata below. One horizon only, in this great 
Upper Cretaceous and Lignitic series, is well marked, and that is fixed as 
definitely as any geological mark of time can be. The yellow arenaceous 
beds of No. 5 are almost everywhere recognizable, and with them the 
lower sandstone of the Lignite formation is at least physically connected. 


* U.S. Geol. Surv. Territ., 1869. p. 50. 
+ Hayden U. S. Geol. Surv. Territ., 1867-69. p. 121. t Ibid., p. 197, 

