











AGE OF THE LIGNITE FORMATION. 185 
Animal life of a form hitherto scarcely represented, is by the changed 
ins! circumstances brought prominently forward, and adds much to 
the apparent completeness of the replacement. It was an appreciation 
of this fact, which led a few years ago to the extreme statement, that 
the Cretaceous period still exists in the deep sea. 
436. In the interior region of America, no great physical break took 
place at this time, and though the change in facies of life forms there, is 
probably much more rapid than can be accounted for without adding the 
acceleration due to physical change, the latter advanced slowly and 
uniformly, and, as might be foreseen, no distinct separating paleonto- 
logical line can be drawn. As geological knowledge increases, it 
is found that its record of time in any one locality is much more 
imperfect than had been supposed. A combination of the records of 
all regions would, no doubt, suffice to fill the gaps, and the Lignite 
formation of America appears to go far to close one of the greatest of 
them. 
437. Dr. Hayden, who has been actively engaged in working out 
the geology of the great area west of the Mississippi, included in the 
Territories, has affirmed and reiterated his belief, that the whole of the 
lignite-bearing rocks of the west belong to one great connected series, 
however separated now in some regions by the upheaval of mountain 
chains, or by denudation.* This view is also insisted on by Prof. 
Lesquereux for a great majority of the different localities, + and is ap- 
parently accepted by Prof. Cope and others. The evidence is also irre- 
fragable that these rocks, wherever their relations are clearly shown, 
or have been carefully worked out, rest directly on the upper member of 
the well marked marine Cretaceous, in a perfectly conformable manner. 
The underlying rock is invariably, or almost invariably, the yellowish 
arenaceous clay or sandstone referable paleontologically—wherever that 
criterion admits of application—to Meek and Hayden’s 5th group, and 
entirely distinct in appearance from the greater part of the beds asso- 
ciated with the lignites above. { I can not find in the reports of the U. 
S. geologists, mention of the occurrence, in the Rocky Mountain region 
or eastward, of beds of lignite or coal in the lower weil-marked members 
of the Cretaceous, comparable to those of the Saskatchewan, which are 
provisionally placed on that horizon by Dr. Hector; with the possible 
exception of the coal observed by Prof. Marsh on the south side of the 
* Am Journ. Sci, and Arts, 1868. U.S, Geol. Surv. Territ., 1870, p. 165. U.S. Geol. Surv. Territ., 
1872, p. 14, &c. t Ibid., p. 350, t Hayden. U. §, Geol. Surv, Territ., 1867-69, p. 121, &e. 


