Bibliographical Notice. 491 
sea retreated from the area it had invaded at the commencement of 
the Cretaceous period; and this retreat would seem to have been 
considerably rapid, from the fact that over most of the area covered 
by the Cretaceous sea we find no evidence of the deposition of the 
of the Tertiary, the Eocene. In the region east of the er 
on the shores of the Gulf and Atlantic, the Eocene beds form a con- 
except in Calif 
a great part of the coast-mountains and cover the base of the Sierra 
Nevada, they are altogether of freshwater origin. In the area of 
the Great Basin, between the Sierra Nevada and the Rocky Moun- 
tains, these lacustrine deposits are =— developed; and in the 
region of the plains they extend in a series of local shies asins from the 
north line of Texas far up into the British Possessio 
** Conclusive evidence of the progressive ovation of this portion 
of our Continent is afforded by the observations of Dr. Hayden, who 
found the lower beds of some of these freshwater deposits containing 
water sediments. During this elevation, the arm of the sea, which, 
in the P eene and early Tertiary ages, extended up the valley 
of the Mississippi to and beyond the mouth of the Ohio, gradually 
prise] and the Tertiary beds were left as parallel belts of de- 
posit from its waters, covering a V-shaped area along the lower 
yam RA including the eastern portion of Arkansas, the State of 
Louisiana, the western and southern portions of the State of Missis- 
sippi, and e reaching around along the coast up on to the 
Atlantic shore. In the Miocene epoch, therefore, our continent had 
nearly the outlines which it exhibits at the present time, and the 
topography of the eastern portion remained almost unchanged. At 
ti 
jointa, upon which the plates of the continent turned. 
* These mountain-masses were not wholly submerged during the 
Silurian period; but the Carboniferous sea swept over nearly all parts 
of them. In the great Cretaceous subsidence they were but partly 
covered ; and since then they, with the tablelands which they crown, 
have remained far above the sea and the general level of the conti- 
nent, and, exposed to atmospherie erosion during all subsequent 
ages, now exhibit the most rd evidences of the potency of this 
agent to be found upon the earth's surface. 
* From the freshwater coms Tertiaries to which I have referred, 
Dr. F. V. Hayden has obtained a magnificent series of fossil plants, 
