82 PALEOZOIC FISHES OF NORTH AMERICA. 
It is evident that these quick-moving fishes, though powerless to injure the 
Placoderms by direct attack, were effectually protected by their celerity 
from their heavily armed enemies or rivals; and as they increased in num- 
bers, they made a desert around their antagonists, and gradually exterminated 
them by the most powerful of all weapons, starvation. 
Section A:—FisHes oF THE CHEMUNG GROUP. 
The Chemung group includes a series of mechanical sediments, cou- 
glomerates, sandstones, and shales, which in my judgment form the true 
base of the Carboniferous system. They are best developed in western 
New York, western Pennsylvania, and West Virginia, where they attain a 
thickness of from 2,500 to 3,000 feet, but thin rapidly and grow fine toward 
the west, until in central Ohio they are locally wanting, and never attain a 
thickness greater than about 100 feet. In Illinois this sheet of land-wash 
is represented by the Kinderhook group, clay and fine sand mingled with 
caleareous matter and having no considerable thickness. 
The fossils of the Chemung are marine, and yet the formation contains 
no limestone, as the proportion of land wash to organic material was greatly 
preponderating. It is evidently a shore deposit laid down along the coast 
of the Alleghany belt of land during a period of subsidence. This subsi- 
dence is proved by the fact that the mass is ripple-marked from top to 
bottom, many of its layers are sun-cracked, bored by annelids and strewed 
with sea-weeds, like so many other sea-beaches. At numerous localities 
these evidences of shore conditions may be found running through 2,000 
feet or more of beds which must have been successively at the sea level. 
The sea rose and fell upon this, and hundreds of streams were busy for ages 
bringing down from the high lands sand, gravel, and clay, which seem to 
have filled the basin about as fast as its bottom sank. Along this old shore’ 
line some of the gravel beds were composed of very coarse material, such 
as could not have been transported far from its place of origin, which was 
the belt of high lands now represented by the Blue Ridge. As we learn by 
faults, 20,000 feet or more of rock were taken from these high lands to make 
the strata which were forming in the interior basin. 
