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 : 



A. Drift clay, 5-12 feet. 



B. Snowy gypsum, 0-5 feet. 



C. Limestone, 1 foot. 



D. Snowy gypsum, 6 feet. 



E. 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, etc. 



