On the Physical Geology of the United States, Sc. 3 
more rapid flow, while the slates and shales whose particles are 
very minute, and would remain long in suspension, required still 
and nearly tranquil waters. 
The limestone deposits have been formed in the thickest masses, 
where circumstances were favorable to the life of testaceous and 
radiated marine animals, of whose remains they are in part com- 
posed. Thick strata of limestone which are continuous and of 
the same geological age, abound with marine relics in one portion 
of the country, and are nearly destitute of them in another. It 
is therefore probable that although organic secretion azded in the 
formation of the limestone, it is not the sole cause. 
Testacea and Radiata are also found in some of the sandstones 
and slates, but they are comparatively rare. The sandstones and 
slates, however, are frequently found to contain abundance of the 
remains of the vegetable kingdom. 
All this great mass of rocks over an area of more than a mill- 
ion of square miles, and several thousands of feet in thickness, 
is composed of the wrecks of older rocks (except the parts of or- 
ganic origin) that have been disintegrated, ground up by attrition, 
washed away and deposited from suspension in water over the 
vast area where we now find them. Each layer of these rocks 
must once have been the bed of the ocean, over which at suc- 
cessive times and under modified circumstances, these various 
materials have been deposited in succession, to form the immense 
mass now exposed to the observation of man, many of the strata 
of which are some hundreds of feet above the level of the sea. 
It is evident that these rocks were formed in the ocean, for the 
following reasons. 
Ist. They are filled with the relics of animals such as are 
analogous to those living in the sea, and not to those of the fresh 
water. 
2d. These relics are so perfect that many of them must have 
lived, died, and been entombed where we now find them. 
3d. The materials of which the rocks are composed, are such 
as are commonly transported, and held in suspension and solution 
in water. 
Ath. The oblique lamination of the sandstones shows the di- 
rections of the currents that deposited them. 
5th. At almost every point of the area mentioned, where deep 
borings have been made far below the flowing waters of the ad- 
