84 PALEOZOIC FISHES OF NORTH AMERICA. 
form; the sea advanced and retreated many times, laying down now sheets 
of gravel (the ruins of the quartz veins of the eroded land), now sand (finer 
fragments of the same), and again shales, of which the materials were sup- 
plied from the argillaceous rocks and were deposited in deeper water. 
From these facts it will be seen that the Carboniferous limestone and 
the Chemung rocks were largely synchronous, but the conditions under 
which they were deposited were different, and few of their fossils are the 
same. In the turbulent water of the shallows and in the bays and estuaries 
groups of mollusks and fishes lived which were quite different from those of 
the open sea. In the latter Sharks predominated and thickly strewed the 
sea bottom with their spines, teeth, and dermal tubercles. Along the shores 
were also Sharks, but with them greater numbers of scaled and plated Ga- 
noids. The remains of these fishes are found dismembered, scattered, often 
rolled and worn in the sandstones or conglomerates. In the Berea grit of 
the Waverly we not unfrequently find entire fishes; small tile-scaled 
Ganoids washed upon the old beach and buried in the sand; in the Che- 
mung nothing but fragments have yet been obtained, the plates, generally 
broken, of Placoderms, Dinichthys, Holonema, ete., the spines of Sharks, 
especially Ctenacanthus, the scales of Holoptychius, and the detached palate 
teeth, often rolled to pebbles, of the Dipnoans, Ctenodus and Heliodus. 
From what has been said of the physical history of the Chemung group 
it is evident that it marks a great break in the order of nature in the eastern 
portion of the North American continent, and that it is the record of a 
period of subsidence which succeeded a long interval of progressive eleva- 
tion, during which the Hamilton group was laid down. We have also seen 
that the ocean into which the materials composing the Chemung and Wa- 
verly were washed was the Carboniferous ocean, and that in its deeper por- 
tions the Carboniferous limestone was forming at the same time that the 
great banks of sand, gravel, and clay of the Chemung and Waverly were 
accumulating in the shallower parts. 
Gnly an imperfect view has yet been obtained of the very rich fish 
fauna of the Chemung group. Nothing was known of it, indeed, until 
about 1860, when Mr. Andrew Way, of Franklin, Delaware County, N. Y., 
discovered some bones and teeth of fishes in the Chemung rocks near his 
