194 GEOLOGY OF OHIO. 
Salina Group.—The Waterlime is immediately underlain by a series 
of calcareous shales and beds of gypsum, which apparently represent the 
Onondaga Salt group of New York. The gypsum quarries worked by 
Mr. George A. Marsh on Sandusky Bay lie within the limits of Ottawa 
county, but the same formation extends under Sandusky, where it has 
been reached in boring wells for oil, at too great a depth, however, to be 
profitably worked. These beds of gypsum also form the bottom of the 
Lake off the south point of Put-in-Bay Island, so that they apparently 
underlie a large area in this vicinity. They deserve to be carefully 
sought for, as they may be found in localities where they will be readily 
accessible. From the continuity of the surface clays, this exploration, 
however, can only be effected by boring. The gypsum of Sandusky is 
of excellent quality, and the quantity is apparently inexhaustible. 
About ten thousand tons per annum are produced at the quarries of 
Mr. Marsh. * 
* The gypsum occurs at Mr. Marsh’s quarries in horizontal strata, of which the 
upper is covered by Drift clay, has been very much eroded, and its normal thickness 
is not determinable. This is underlain by a stratum of limestone one foot in thick- 
ness, beneath which is another stratum of snowy gypsum six feet in thickness. 
Below this is another limestone band one foot in thickness, and a third stratum of 
snowy gypsum, which has been excavated to the depth of about six feet and has 
not been passed through. The subjoined wood-cut will give a better idea of the 
deposit than any verbal description: 
oes hat ae ss ab So 
Ie : ae aS ee 
es 
E MALLE 
a 
A. Drift clay, 5-12 feet. D. Snowy gypsum, 6 feet. 
B. Snowy gypsum, 0-5 feet. E. Limestone, 1 foot. 
C. Limestone, 1 foot. F. Snowy gypsum, 6 feet. 
‘The bands of limestone interstratified with the beds of gypsum in the above section 
afford conclusive evidence that the gypsum was not produced by the action of acidu- 
-lated waters on limestone. This theory of the genesis of gypsum has been advocated 
by high authority, but all the great deposits which I have seen were certainly not 
formed in this way, but rather by precipitation from basins of water charged with 
Salt, sulphate of lime, ete. 
