102 Eeport op the State Geologist. 



The highest points in the* county are about Prospect hill, and 

 may be estimated (no data being on record) at 1,200 or 1,300 feet 

 above tide = say 800 feet above Seneca lake. From this it 

 appears probable that the highlands of the southern part of the 

 county fall short of the uppermost Portage beds by several hun- 

 dred (400?) feet. The thick-bedded sandstones of the highest 

 beds do not appear on these hills. 



Thickness and Dip of Rocks. 



The necessity of revising our estimate of the thickness of the 

 formations of central New York has been pointed out by Prosser 

 in the American Geologist for October, 1890. 



For the Salina group we have the evidence of several wells 

 drilled f-or gas, which give a probable thickness of about 1,000 

 feet, the southernmost well indicating an actual 980 feet. At 

 Geneva the I^ester well went 1,'400 feet to the Niagara ; from 

 which must be subtracted the thickness of the Corniferous and 

 part of the Marcellus, say 100 feet, leaving a probable 1,100 

 feet. 



The thickness of the Upper Helderberg, as far as exposed, is 

 32+8+2=4:2 feet, but is doubtless considerably greater. These 

 figures represent the Avery quarry, the Waterloo river stone and 

 the Onondaga limestone at McQuane's. 



The Corniferous limestone measured at the Ithaca well 78 

 feet. 



The Marcellus can not be closely estimated. Clarke considers 

 it about 100 feet thick in Ontario county, but farther west its 

 upper limit becomes very uncertain. Ithaca well, 82 feet. The 

 Hamilton was estimated by Hall at " not less than 1,000 feet" in 

 this region. The Ithaca well gave 1,142 feet. The distance 

 from a mean point in the Hamilton to Ithaca is 25 miles ; that 

 from a mean point in the Salina to Ithaca is 42 miles ; and the 

 change in the thickness is very great, being perhaps at Ithaca 

 twice what it is at Seneca Falls. 



The Tully limestone is not far from 12 feet in thickness. In 

 Ithaca well it was 30 feet, with which compare S. G. Williams's 

 statement that the thickest outcrop at Cayuga lake measures 18^ 



