. 810 Dr. Hayden on the Period of Elevation of the 
Of course, as the land was slowly elevated toward the surface 
of the waters, the newer Tertiary beds would be subjected to 
the erosive action of water first, and thus continuing downward 
mass was slowly rising, until the granitic nucleus was ex- — 
h 
e 
elevation. Although the lignite Tertiary beds are developed in 
full fo ong the base of the larger ranges of mountains, 
it is not unlikely that some of these ridges formed. barriers or 
lofty shores to aa great Tertiary lakes. It would seem. as if 
is country during the Tertiary period was not unlike the Un- 
dine region of the north, so called by the geographer Nicollet on 
account of the great number of fresh water lakes distributed over 
that district. 
often lie quite high upon the slopes of the mountains conform- 
ing to the Cretaceous rocks and sometimes inclining at a high 
and the Sweet Water mountains on the North Platte they at 
while the intermediate yielding beds of clay, sand, and lignite, 
are clothed 
by the White River group, the same features are seen, thot ‘i 
the strata incline less, being more remote from the anticlin 
érest, On both sides of the Wind River mountains the same 
phenomena occur, and other examples might be cited pointing 
to the same conclusions, but enough has been said to show that 
_ itis probable that the lignite Tertiary beds partook of the same 
movements that have elevated the older fossiliferous rocks. We 
therefi : the fracture of the earth’s crust in this Por 
tion of the West, by which the nucleus of the mountains w% 
ee eared mas ye time of the accumulation of the lig 
nite deposits or at the close of that epoch, 
, although there is not a IPRs a between 
e lignite beds and the Wind River group, the latter i 
direction only at a much smaller angle. Neat 
ae 
