Haworth. | Physical Properties of the Tertiary. 281 
ever, we adopt the more rational view that the materials were prin- 
cipally accumulated by river action throughout a period extending 
from the earliest indicated by paleontology to the present the above 
difficulties disappear. 
ORIGIN AND MODE OF FORMATION OF THE TERTIARY. 
From what has already been given it will be seen there is little 
if any room for doubt regarding the source of the Tertiary material. 
It has principally come from the great Rocky mountain area to the 
west. Portions of the mountain area have been dry land from early 
geologic times, and the weathering agents have acted upon such in 
the usual manner producing the ordinary products of decomposition 
of crystalline rocks, such as sand, pebbles of various sizes, ete. It is 
probable that throughout the main period of geologic history the 
elevation of these dry land areas was so small that the drainage 
carried away but a small proportion of the debris thus produced and 
that as a result an extraordinary amount of it was ready for trans- 
portation as soon as the elevation became sufficient to produce a 
considerable fall. It need not be doubted that a part of the Tertiary 
material was obtained from the underlying Cretaceous, but examina- 
tion shows that this constitutes but an unimportant part. When 
the final elevation of the whole mounainous area was effected and 
the drainage became established across the great plains area to the 
Mississippi, the eastward migration of great quantities of debris 
began. 
Mode of Deposition—Formerly geologists thought that the Ter- 
tiary of the plains from north to south was deposited under lake 
water, that large inland fresh water lakes were formed at different 
places as a result of the mountain drainage not reaching entirely 
across the plains. The Tertiary formations in different places in 
the west have uniformly been explained in this way. The applica- 
tion of such a mode of accumulation to the great plains has rarely if 
ever been questioned so far as our literature shows. In his “Report 
on the Fortieth Parallel,’ King! states that a large portion of the 
1 Vol. I, p. 451. 
