GEOLOGIC MAP OF THE TULLY QUADRANGLE 41 



ward. In the Solvay salt wells in Tully valley the Oriskany sand- 

 stone was found to be 15 to 1 8 feet thick and it is 18 feet thick at the 

 Corrigan quarry on the Skaneateles outlet. East and west of this 

 area the rock thickens and thins, sometimes entirely disappearing 

 from the succession as at Split Rock quarry where it appears at one 

 end of the quarry and is absent at the other. This succession of 

 lentils begins in the eastern part of the State and gradually disap- 

 pears westward and from Ontario county to Lake Erie it is simply a 

 thin continuous mantle of sand, sometimes quartzitic, which has evi- 

 dently been washed from a shelving and eroded shore extending as 

 far as Buffalo. 



The fossils of this rock are those found more abundantly in the 

 better development of the sandstone as at Oriskany Falls and Yaw- 

 gers woods. Union Springs. Spirifer arenosus is common 

 as well as Leptaena ventricosa, Hipparionyx 

 proximus, M e r i s t e 1 1 a lata and a few other forms. 

 Rensselaeria ovoides, one of the index fossils of the 

 horizon, is rare in this vicinity. 



Onondaga limestone 



This important limestone formation attains a thickness of 65 to 70 

 feet, increasing slightly from east to west. It is a series of light 

 bluish gray, glistening, semicrystalhne limestone strata in even con- 

 tinuous layers from 1 inch to 2 feet, 6 inches in thickness, separated 

 by thin seams of dark calcareous shales. Many of these layers are 

 highly pure limestones but others ndt confined to any particular 

 horizon are shaly and more or less impure. Flattened nodules of 

 dark blue or black chert, sometimes in continuous sheets, occur 

 unevenly distributed throughout the entire mass, though most com- 

 mon in the upper part. In the region west of the area under con- 

 sideration the lower beds of this limestone are usually comparatively 

 free of chert and are highly abundant in corals, these corals having 

 formed very extensive reefs along the shore of the ancient continent, 

 but this is a characteristic not continuous throughout the sections 

 of the formation in the State and from here eastward the lower 

 layers contain considerable amounts of chert, rather uniformly dis- 

 tributed through the entire mass of the limestones. Formerly the 



