156 
GEOLOGY OF THE FOURTH DISTRICT. 
as well as Crinoidea also existed, but of all these we only find fragments, which bear evi¬ 
dence of being broken and worn previous to imbedding. In these situations fossil shells are 
few, and it is only when the mass is more evenly distributed that they increase in number. 
Now all these circumstances seem plainly to indicate that at these points of thickening 
there was a part of the ocean bed, on which these corals had established themselves, and on 
which they continued to construct their habitations for a long period, as the great size of many 
would prove. In the more sheltered portions smaller and more delicate forms, with the Cri¬ 
noidea seem to have flourished; the latter in great perfection, judging from the size of the 
columns. The more exposed portions and the more fragile kinds were broken down as they 
came within the influence of the waves, and these materials were spread around the base, 
the coral reef extending in every direction as far as the material was transported, and 
there we now find the mass thinning out. . There seems in this nothing more than we might 
expect, and probably only what is now accomplished in coral reefs which are near the surface 
of the ocean, and which may be alternately elevated above or depressed beneath it. The 
great amount of destruction here visible was not all accomplished at once, for we may find an 
overturned mass of coral covered with a fine deposit, and upon this another mass of coral, 
either overturned or in its natural position, the whole indicating a long continuation of the 
causes in operation. The simple fact of the succesive growths of coral upon deposits cover¬ 
ing other corals, of itself proves a great lapse of time; for the growth of all these forms is 
exceedingly slow. 
From the amount of exposure, it is impossible to ascertain whether these coral reefs were 
circular, or whether they formed more than a single line skirting the margin of the ocean. 
From the great amount of denudation on the north, and the east and west extent of these coral 
banks, we may infer that there was more than a single range; and if it can be proved that 
they existed far south of the present outcrop, we may rationally infer that they formed a series 
of circular reefs, probably much in the same manner that similar reefs and islands are formed 
in the present ocean. 
The Onondaga limestone is scarcely anywhere developed in the same perfection as in the 
First and Third Districts, where it contains a greater number of fossils, and as a distinct mass 
is more persistent. As a quarry stone for building and other purposes, it rarely appears in 
the perfection which it assumes at Syracuse, Le Roy being the only known locality where 
this character is possessed in an equal degree ; while in most other places where it is suffi¬ 
ciently compact for that purpose, the strata are very thin. 
Localities. — The examination of a few points in the district, will suffice to acquire an ac¬ 
quaintance with this rock. The first locality of interest is at Vienna, where its connexion 
with the rocks above and below are clearly seen. Two miles northwest of the same point, it 
is better developed, and contains its peculiar fossils. Caledonia offers the next point of muck 
interest, though the towns of Rush and Mendon, on the east side of the Genesee, are inte¬ 
resting in some degree. Le Roy, at the quarries before alluded to, offers the best exhibition 
-of this rock in the district. In Clarence there is also a good exposure, a mile west of the 
