ONONDAGA LIMESTONE. 
153 
group. That such is the fact however appears plain, for there are many fossils of the lime¬ 
stones above the salt group, which are identical with the Wenlock formation, while the iden¬ 
tity of so many species in the Niagara group leaves no doubt of perfect correspondence. We 
are therefore to look upon the salt group as a formation, on this continent, coming in at a pe¬ 
riod during which, in England, the rocks are supposed to belong to a continuous group, or to 
be parts of one formation. 
The Onondaga limestone in many places contains nodules, or thin interrupted layers of 
chert or hornstone (usually called flint); and sometimes the Favosites are partially dissolved 
and the cavities lined with silex in the form of chert, chalcedony or crystals of quartz. The 
alimentary canal of the crinoidal columns is frequently lined with crystals of quartz, and the 
chambers of Orthocera, as well as the cavities of other shells, often present the same appear¬ 
ances. 
Its characteristic features, when well developed, and which are always much more prominent 
than the lithological or mineral characters, are the presence of Cyathophylli, Favosites, and 
fragments of crinoidal columns. These always accompany it in situations where it is suffi¬ 
ciently developed to be of much importance either in economical consideration or geological 
interest. 
In Seneca county this rock is scarcely visible, or forms only a very subordinate layer and 
destitute of its characteristic fossils. In the adjoining county it becomes of more importance, 
first appearing as a thin layer near Oakes’ corners, and along the terrace to East-Vienna; at 
the latter place it appears in the bed of the creek resting directly on the Oriskany sandstone, 
and succeeded by the cherty layers of the corniferous limestone. It is but a thin mass at 
this place, being little over two feet thick. At another point southeast of this the Onondaga 
limestone is entirely absent. 
At Wayland’s quarry, northwest of Vienna, this limestone appears in several strata following 
the water-lime, and marked by its characteristic fossils. A short distance to the southwest 
of this quarry it appears again, containing Favosites and other fossils. The rock at all these 
places is compact, of a greyish blue color and less marked by seams of shale than in many 
other places. 
At Manchester and in the bed of Mud creek at Freedon it is but slightly developed, being 
a thin layer of a greyish blue color and destitute of fossils. It retains the same character as 
far as Mendon in Monroe county, where it is better developed and contains a larger number of 
corals and Cyathophylli. It has also the same character, or is even more fully developed, in 
the town of Rush, where it disappears before reaching the Genesee river. 
On the west side of the Genesee, it appears at Caledonia, still a thick compact mass, with 
a few thin layers separated by shale, and containing a great number of Cyathophylli, Favo¬ 
sites, and other fossils. For some distance north and west of this place, it maintains the same 
character, and the surface is strewed with fragments which contain its typical fossils. 
North of Le Roy village, on Allen’s creek, the rock resting on the Onondaga salt group is 
a compact sub-crystalline greyish blue limestone, containing no fossils ; this is succeeded by 
[Geol. 4th Dist.] 20 
