GLACIAL WATERS IN CENTRAL NEW YORK 1 3 



attributed to the sinkage of the superficial strata by the removal 

 of the underlying salt and gypsum beds through solution [see 

 title 8]. South of this parallel in the Genesee and Oatka valleys 

 are the mines of rock salt and the factories using the brine. 



All the ground between Mumford, Caledonia and Leroy is much 

 broken by sinks and sink ridges, of varied dimensions. The 

 ridges vary from doubtful irregularities of the surface up to sharp, 

 broken anticlines sometimes 10 or even 15 feet in hight [see pi. 10]. 

 Some of the ridges are short and irregular, many long and winding. 

 Perhaps the more extended are east and west in trend, or along 

 the strike of the rock. The higher and steeper ridges in places 

 resemble scarps due to differential weathering, and some even 

 resemble in form wave-cut cliffs or stream banks. On first inspec- 

 tion the forms would be liable to varied misinterpretations. 



These sinkage structures are not only postglacial but subsequent 

 also to the glacial drainage, as they have broken up and obscured 

 the channels. It is suggested that the removal of the soil cover by 

 the glacier, along with some of the superficial, weathered rock, and 

 the subsequent removal of the glacial drift by the ice border rivers 

 exposed the fissures in the strata. The rivers and the subsequent 

 lakes (Warren and Dana) supplied a large volume of water during 

 many centuries for the subterranean circulation and probable 

 removal of a portion of the lower limestone beds and the under- 

 lying gypsum. 1 Conspicuous ridges lie along the north side of the 

 highway midway between Caledonia and Leroy for a stretch of 2 



1 Bearing on the origin of the sinkage features the following may be noted. 



The surface rocks of the area are Onondaga, limestone, beneath which occur in descending 

 order Cobleskill limestone; Bertie waterlime; Camillus (gypsiferous) shales. The gypsum 

 beds lie less than ioo feet below the surface, and are partly above the present surface drainage 

 on the north. Below the base of the Onondaga the depth of the salt is 440 feet at Leroy 

 and 486 feet at Caledonia. The thickness of the salt beneath Leroy is given as 15 feet; and 

 it lies 253 feet above sea level. At Caledonia the highest salt bed is at or below sea level, 

 and south of the parallel the beds are considerably below sea level, due to the southward 

 dip of the strata. Considering that the salt is not only below the level of free circulation 

 but covered by hundreds of feet of quite undisturbed shales the chance for rapid removal 

 seems small. On the other hand the gypsum and the limestones are exposed to subsurface 

 waters with clear drainage. It is important to note that both here and at Syracuse the 

 sinkage has been observed only in the belt along the summit of the Onondaga escarpment. 



The parallel of Caledonia and Leroy is the northern edge of the salt-bearing area, the 

 sinkage structures extending a mile or two north of the line. South of the parallel the salt 

 beds increase in thickness, along with the increasing depth below sea level. It has been 

 thought that the present northward limitation of the salt was the original limit of the deposits, 

 but the possible removal of some portion of the northern edge of the beds should be considered. 



A point worthy of consideration is the possible amount and the form of the surface dis- 

 location that would be produced by the slow removal of even some scores of feet of salt 

 beneath more than 400 feet of rock, mostly shales. The writer concludes that the irregu- 

 larity and the sharp relief of the sinkage features indicates the subsidence of only a 

 moderate thickness of rock — perhaps 100 feet. 



