C0RN1FER0US LIMESTONE. 
165 
taining the same fossils as at Vienna, and in addition I obtained an Ichthyodorulite about six 
inches in length. Some part of the rock above this is very light colored, resembling the upper 
part of the Onondaga salt group. This portion, however, is marked by the presence of one 
of the most characteristic fossils of the rock, viz. Odontocephalus selenurus. The higher 
strata are thin-bedded, but with little intermixture of shaly matter. 
The lower part of the rock above Freedon is a fine-grained, compact blue limestone, with 
a moderate proportion of hornstone. It contains some thin beds of coarser, greyish, sub¬ 
crystalline limestone; and it is these which in some places become augmented in thickness, 
and furnish the fine quarries in this rock. At this place they distinctly alternate with the blue 
strata. This character is the same as that presented in the lower part of the rock in Seneca 
county, but it offers no sufficient reason for a subdivision. 
Where best developed, the rock presents the threefold division visible on Flint creek and 
Mud creek. The same may also be seen in a few other places, but the distinctive characters 
are either not persistent, or they are not visible through the whole district. The very fine 
grain and light grey color seen in part of the mass on Mud creek, is also visible at one or two 
other places, but it is far from being a general or important character. 
At Farwell’s Mills, and at West-Mendon, the same general character of the rock is exhibited. 
The proportion of hornstone varies at almost every locality, but usually some of the strata 
consist in large proportion of that mineral. At Avon the higher strata of the rock have be¬ 
come a compact thick-bedded stone, and being entirely free from hornstone, are quarried in 
considerable quantities. The lower part of the mass has been exposed near the same place, 
and contains abundance of hornstone. 
It is quite unnecessary to follow all these local variations in the character of the rock. From 
what is already said, it will be plainly seen that the nature and proportion of the component 
parts vary at different localities. In some places the hornstone predominates through more 
than half the mass, while in others it is in very subordinate proportions. 
On the west side of the Genesee, its cherty characters are better developed than elsewhere. 
Between Caledonia and Le Roy, there are many acres, and I believe hundreds of acres, which 
are literally paved with hornstone in small angular fragments, or larger masses united by car¬ 
bonate of lime. In consequence of this stony surface, this part of the town was for a long 
time considered almost useless for agricultural purposes, though originally it produced a good 
growth of timber, and more recently it has been discovered to be very productive, affording 
some of the finest crops. From the nature of the rock, the soil is necessarily highly calca¬ 
reous ; and from the abundance of stones, the surface is kept at a more equable temperature 
than in some other soils. 
The manner of destruction produced by weathering is very obvious in this rock : the cal¬ 
careous matter dissolves away ; the hornstone, as it projects, shows little interstices or cracks, 
which are soon filled with water, which, on freezing, enlarges the space, and thus after a time 
the whole mass is broken down. This process is readily understood by an examination of the 
rock at any of its outcropping points. The roads over this portion of the rock are superior to 
