Bibliographical Notice. 489 
slight, and resulted in the addition of but a narrow margin of Cre- 
taceous rock, much of which has doubtless been cut away by the 
waves of the ‘Atlantic, extending from Martha’s Vineyard around our 
Atlantic and Gulf-coast to Mexico. The north-eastern portion of 
the continent seems not to have shared in this depression, as no Cre- 
aedes rocks have yet been found there. West of the Mississippi, 
ico, and 
vered by its caleareous i beccud . Suffice it to say that over a 
well = its fossils, prove that it is sate of the immediate débris 
of the land, and it was gradually submerged beneath the ocean— 
m Soke leaves, trunks > — &c.,—and is, in fact, simply an 
unbroken series of sea-beac 
« These coarser beds are Saeed, in the ascending series, by 
strata of more or less pure limestone, iun. Masi with charae- 
teristic Cretaceous Mollusks (Znoceramus, Ammonites, Baculites, &c.), 
the natural aecumulation from the waters of the ocean, and form ing 
a marked contrast with the mechanical sediments and terrestrial 
fossils of the underlying beds. 
. That the encroachment of the ocean was from the east and south 
towards the Rocky Mountains is proved by the fact that as we go 
from Texas and Arkansas in that rection, we find the limestones. 
becoming less pure, containing more inorganic id (sand and 
clay), until in New e ert Colorado but little true limestone 
ed in the whole format 
uring this rubmergenee there was oceanic communication be- 
b 
through the British Possessions. All the eastern half of the con- 
tinent was; however, out of water, for we find no Cretaceous 
alif 
little way up the flanks of the Sierra Nevada, and in some portions 
of ~ Rocky-Mountain country no traces of these rocks can be 
foun 
rE o Plants to which I have referred as forming the characteristic 
fossils of the Lower Cretaceous beds are of special interest, as they 
open a new chapter in the botanical history of the world. Altho 
the region which furnishes them has been but partially surveyed, 
and collections made under the most unfavourable circumstances, 
already fully fifty species of forest-trees are represented in these 
