ONONDAGA LIMESTONE. 
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village of Clarence Hollow. Near Williamsville, on the farm of Mr. Youngs, a large number 
of the corals and other fossils of the rock may be obtained; and this locality, with Clarence 
and Le Roy, are by far the best in the district. 
Thickness. — The thickness of this mass is very variable, being from one foot to twenty or 
even forty feet. At Black Rock, the stratum representing this rock is fourteen inches thick; 
in Newstead, Erie cbunty, about the same; at Vienna, two feet. At Williamsville, as nearly 
as can be ascertained, it is twenty feet. This point and Le Roy, where the thickness was not 
ascertained, present the greatest development. 
Mineral contents. — The only minerals noticed in this rock, are crystallized carbonate of 
lime, quartz in crystals lining cavities, chalcedony and hornstone, with iron pyrites in a few 
places. The Favosites are often silicified, and their cavities lined with small crystals of quartz. 
This rock is so intimately connected with the next in succession, and forms surfaces of so 
little extent, that its characters in agricultural respects can scarcely be considered, but will 
be noticed in connexion with the rock next in order. 
Organic Remains of the Onondaga Limestone. 
The organic forms of this rock are its most prominent marks, wherever the mass is well 
developed. In the Fourth District, Corals and Crinoidea were the predominating forms, the 
conditions under which it was deposited being apparently unfavorable to the existence of 
Testacea. A few univalve shells have sometimes been found, and more rarely some species 
of Atrypa and Delthyris. 
Among the numerous forms of corals, those of the three following illustrations have been 
selected, as being the most common or most obvious among them. The number may be 
quadrupled, without exhausting the species of this rock. 
61. 
1 and 1 «. Favosites alveolaris. 3, 3 a and 3 b. Fragments of column and joints of 
2, 2 a and 2 b. F. Gothlandica. unknown Crinoidea. 
