Geological Observations.— Reagan. 237 
over to the White river — Oak creek side. It will necessi- 
tate more research work, however, to determine this fact. 
The Recent formation (not mapped ) extends out on the 
bluffs on either side of White river for quite a little distance. 
It is the surface rock in all the valleys wherever the valley 
widens out. Along White river and Little Oak creek it 
covers the meander region. The bluff formation is proba- 
bly Champlain in age, some being probably even Glacial. 
The formation in the valleys is more recent and extends in 
time to the present. Little Oak creek is now building up 
its lower valley ; and White Thunder creek its valley in its 
middle course. . The whole formation, whether in the val- 
ley or on^the bluffs, is of river origin. 
To this age of rocks seems to belong the Tertiary debris 
from the broken down mesas and bad lands. Though 
patchy, this debris covers at varying thicknesses a consid- 
erable part of the area marked Cretaceous ; the Tertiary, 
however, is not in "situ" nor in thickness enough to deter- 
mine the surface age. 
Resume: As the Cretaceous period neared its close the 
surface of the region became dry land and was such for a 
long period as is shown by the then eroded surface. The 
region then, in Oligocene times, began to fill with debris of 
the gravelly cobblestone type. Later it apparently became 
laked, and the soft fine-grained shales were deposited. 
While this was going on, fresh-water fish and gigantic tur- 
tles skimmed the waves and tropical animals roamed along 
the beach. After a long lapse of time, the region again be- 
came land and was much eroded. Another period of deposi- 
tion then, in Loup Fork times, set in. The whole area was 
flooded with sand. This was deposited at intervals till it 
reached a thickness of more than 400 feet in the vicinity of 
Valentine, Nebraska. Throughout the whole time the re- 
gion seems to have been in a swamp or ponded state. As 
the climate was tropical, there roamed over the marshy 
areas and through the jungles the tiger, horse, hyena, camel, 
mastodon, and the many other tropical animals of that 
epoch, as is shown by their fossil remains. The region was 
left ponded at the close of this epoch. In the succeeding 
epoch the present streams cut their channels to about their 
