332 | J. D. Dana on American Geological History. 
a continent now sunk in the ocean. No facts prove that such a 
continent has ever existed, and the whole system of progress, as 
I have explained, is opposed to it. Moreover, gravel and sands 
are never drifted away from sea-shores, except by the very 
largest of rivers, like the Amazon ; and with these, only part of 
the lightest or finest detritus is carried far awa v4 for much the 
larger part is returned to the coast through tidal action, dea 
has a propelling movement shoreward, where there are soun 
ings. The existence of an Amazon on any such Atlantic con- 
tinent an Silurian, Devonian, or ae times, is too wi 
all. 
‘Paral el with this fact, we find that in South America, as Dr. 
Lund observes, where, in the last age before Man, there were 
the giant Megatherium and Gl Pan , and other related Eden- 
, there are now the small Sloth Armadillos, and Ant- 
eaters. 
So, also, on the Oriental continent, the gigantic Lion, Tiger, 
Hyena, and Elephant, and other monster quadrupeds, have now 
their bea inferior representatives. 
In New Holland, too, o waa of Marsupials, there are Mar- 
supials still, but of less magnitude, 
2, This American onto has contributed to science 4 
knowledge of some of the earliest traces of Re ple ae mio 
of the Pennsylvania coal formation, elaribat by Mr. Kin 
Mr. Lea, and others from the Nova Scotia coal-fields, ‘Secret 
by Messrs. Dawson and Lyell. 
It has afforded the earliest traces of birds thus far deciphered 
in geological etary, ,—the colossal and smaller waders, whose 
tracks cover the clayey layers and sandstone of the Jurassi¢ 
rocks in the Connecticut valley. The earliest Cetacea yet known 
are from the American Cretaceous beds, as described by 
Leidy. And among the large Mammals which had possession 
of the renewed world after the Cretaceous life had been swept 
away, the largest, as far as has been ascertained, lived on n this 
continent. The Paleotheria of the Paris Basin, described by 
Cuvier, were but half the size of the allied Titanotheria of Ne- 
