220 



Report of the State Geologist. 



Tully Limestone. Next above the Hamilton group and cropping out 

 in many places along and on both sides of the southern boundary lines of 

 Madison and Onondaga counties is the Tully limestone, so called from its 

 favorable exposure in an escarpment on the west side of the valley in the 

 town of Tully, Onondaga county. 



It is an exceedingly hard, dark blue-grey limestone, in layers one to 

 three feet thick, some of which are highly schistose, while in others the 

 rock is brittle, breaking into sharp angular fragments. The whole bed is 

 too impure for profitable use in the manufacture of quicklime, and too hard 

 and brittle to be of much value as building stone. 



It is the highest persistent limestone formation in the rocks of the 

 salt district, being separated by more than a thousand feet of soft shales 

 from the Onondaga limestone. 



On account of its isolated position and peculiar characteristics both 

 lithologic and paleontologic, it is easily recognized and its position in the 

 outcrops readily traced. 



Its greatest thickness is about thirty feet, which it attains in the 

 southern part of Onondaga county and in the ravines near the head of 

 Skaneateles lake. 



It is exposed for about ten miles on both sides of Cayuga lake, dipping 

 beneath the water three or four miles from the head, and is also seen on both 

 sides of Seneca lake between Willard asylum and North Hector, and on the 

 Keuka lake outlet, and in several ravines in the towns of Torrey and 

 Benton, Yates county. 



It diminishes in thickness westward from Onondaga county. On the 

 shores of Cayuga lake it is fifteen to eighteen feet thick, and along Seneca 

 lake eleven to fourteen feet ; in the ravine at Bellona seven feet, and at its 

 most westerly exposure which is in the bed of a small stream in the south- 

 west corner of the town of Grorham, Ontario county, it is thirty-one inches 

 thick in two layers, the upper one three inches and the lower one twenty- 

 eight inches in thickness. It does not appear on Canandaigua lake, three 

 miles to the east, though that horizon is exposed for several miles along 

 both sides. 



No limestone occurs in the horizon of the Tully in the western part 

 of the salt district, but the contact line of the bluish grey Hamilton shales 

 with the Genesee black slate is distinctly marked and easily recognized 

 when exposed. Wherever the horizon has been exposed for a length of time, 

 a stain of iron rust makes the contact line more noticeable. This stain is 



