ERIE COUNTY. 7 191 
as the “Sandusky stone,” and largely used for building, paving, and flag- 
ging at Sandusky and elsewhere. The lower portion is light-colored, 
and much more massive, and is that quarried at Kelly’s Island and 
Marblehead. The fossils of the Corniferous limestone are exceedingly 
numerous and of great interest. Like most other limestones, this has 
been derived from the decomposition of organic structures, and in many 
places it is almost altogether made up of corals and shells. In chemical 
composition it is a magnesian limestone, containing twenty per cent. or 
more of magnesia. This peculiarity has been quoted as objectionable in 
its adaptation to the manufacture of lime; but, on the contrary, it is 
benefited by this ingredient, the magnesia making it slower in setting, 
“less hot,” as the masons say, and therefore much more manageable. 
The Corniferous limestone has been so fully described in the first vol- 
ume of our report, both as regards its physical characters and fossils, 
that little need be here said of its general relations. It is proper, how- 
ever, that I should here refer to the views advanced by Prof. Winchell 
in the reports on Delaware and Paulding counties, and which are not 
quite in accordance with those I have expressed in regard to the age of the 
upper, or Sandusky, member of the Corniferous limestone. It is claimed 
by Prof. Winchell that because it contains certain mollusks that are usu- 
ally called Hamilton fossils, such as Cyrtta Hamiltonensis, Sprrifera mucro- 
nata, and Athyris spiriferoides, it must necessarily be Hamilton; but with 
the exception of Spirifera mucronata, which I have never found in the for- 
mation except at its very summit, all the other Hamilton fossils found in 
the Sandusky limestone are such as are also found in the Corniferous of 
New York, and therefore they constitute no reliable evidence of the 
Hamilton age of the deposit. On the contrary, the Sandusky limestone 
contains quite a large number of fossils which are not only common in 
the lower, or Kelly’s Island, subdivision of the Corniferous, but are re- 
garded as characteristic fossils of the Corniferous in New York, and are 
not found in the Hamilton. We also have in the Sandusky limestone 
all the remarkable fossil fishes—alluded to further on, and more fully de- 
scribed in our paleontological reports—which form the most striking 
features of the fauna of the Lower Corniferous (Kelly’s Island and Co- 
lumbus) limestone. None of these have ever been met with in the 
Hamilton of New York. The Corniferous mollusks alluded to above as 
found in the Sandusky limestone are Spirifera acuminata, S. gregaria, S. 
macra, Pentamerus aratus, Strophodonta hemispherica, Tentaculites scalaris, 
etc. Of these, only the first has ever been found in the Hamilton, and 
this, perhaps, but in a single instance in New York, while it is locally 
nearly as abundant in the Sandusky as in the Kelley’s Island limestone. 
