tending back some ten or twelve feet from the front of the 
ledge. This cave, owing to the peculiar conditions by 
which it is being formed, is continually growing larger. 
This growth will, no doubt, at some future time be the 
cause of its destruction, for the limestone will not be able 
to sustain itself indefinitely when supported only by the 
sides and rear. When the strain upon the limestone, due 
to the force of gravitation, has become so great as to over- 
come the cohesion of its particles, the result will be dis- 
astrous to the cave. The appearance of the ravine would 
indicate that such has been the fate of a pre-existing cave 
at some time in the past. 
The more common fossils outside of the two character- 
istic ones already mentioned are: Spirifer Tulltza, S. sudb- 
unzbona, Productella Tulha, Atrypa spinosa, Rhynchonella 
congregata and Chonetes logant (variety) aurora, There 
are also several species of trilobites found, among them 
are: Bronteus Tullius, Phacops rana, Dalmanites calliteles, 
Proetus Row? and P. macrocephalus, 
The limestone is quarried in several places, and used 
for a building stone. It is also burned to alimited extent 
for lime. It makes a good but not avery white lime. 
The Genesee Slate.—Immediately overlying the Tully 
Limestone we find a very black, fine grained, argillaceous 
shale, which is known as the Genesee Slate. 
Its structure is somewhat slaty, hard and brittle, much 
more so than the Marcellus Shale; nevertheless, it is so 
uneven and fissile that we often hear it spoken of as the 
Genesee Shale. 
It forms the tops of some of the higher hills in our 
southern towns, and may be easily recognized by its black 
color and its hard and brittle structure. We cannot easily 
mistake it, because it immediately overlies the Tully 
Limestone, which may always be recognized by its char- 
acteristic fossils. 
45 
