REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1903 105 



the Genesee river, which had not been cut to a great depth. In 

 this way the Niagara escarpment was cut below the level of the 

 col at Kome, so that, when the St Lawrence channel was free 

 from ice, the drainage from the Finger Lakes flowed over the 

 lowest part of the Niagara cuesta into Lake Ontario instead of 

 through the Mohawk to the Hudson. 



Geology. The geologic position of the gypsum beds of New 

 York State has been placed by most geologists in the Onondaga 

 salt group of the Silurian system, or, as it is called, the Salina 

 group. 



Vanuxem describes this group as follows: 



This important group contains all the gypsum masses of 

 western New York and furnishes all the salt wate'r of the salines 

 of the counties of Onondaga and Cayuga. From the point where 

 the Niagara group terminates at the east, it rests upon the Clinton 

 group ; and, as the latter group also comes to its end nea'r the first 

 district, it reposes there upon the Frankfort slate, upon which it 

 continues to near the Hudson river. 



It forms a part of the high range on the south side of the 

 Mohawk; appearing at the north end of Otsego county and in 

 Herkimer and Oneida, being its northern outcrop. It makes its 

 first appearance by the side of the Erie canal at the east end of 

 Madison county, and from thence west the canal was excavated 

 in the group. 



The Onondaga salt group may be divided into four deposits. 

 There are no well marked lines of division between the deposits; 

 but for practical purposes the divisions are sufficiently obvious. 



The first or lowest deposit is the red shale, showing green spots 

 at the upper part of the mass. 2d, The lower gypseous shales, the 

 lower part alternating with the red shale, w^hich ceases with this 

 mass. 3d, The gypseous deposit, which embraces the great 

 masses quarried for plaster, consisting of two ranges, between 

 w^hich are the hopper-shaped cavities, the vermicular limerock of 

 Eaton, and other porous rocks. 4th, and lastly, Those rocks 

 which show groups of needle-form cavities placed side by side, 

 caused by the crystallization of sulfate of magnesia^, and which 

 may be called the magnesian deposit. 



The whole of these deposits are found between Oneida creek and 

 Cayuga lake. To the east of the creek, they do not all occur, as will 

 subsequently be made known. They thin out to the eastward and 

 probably terminate entirely a few miles east of the Hudson river ; 



'Sulfate of lime most probably. [F. J. H. Merrill] 



