56 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



The equivalent of this group in Indiana occurs as the surface rock in 

 a narrow strip on the north and northwest border of the Niagara area north 

 of Indianapohs; also in a small tract in the Ancinity of Logansport, and, as 

 interpreted by Phinney, in a considerable area in the northwestern part of 

 the State. The exposures in Indiana are few on account of the great thick- 

 ness of the drift. This is also the case in much of the Ohio area. 



Lowe- Heiderberg limestone. — The Lower Hcldcrberg lias been separated from 

 the Waterlime in New York and in Indiana, but was classed with it by 

 Orton in his latest report on Ohio. It is an extensive formation in eastern 

 New York, having a thickness of 300 or 400 feet, but it becomes incon- 

 spicuous before reaching the western part of the State. In Indiana, also, 

 it lies mainly outside the region here discussed. It is therefore of little 

 importance to the present discussion. 



oriskany sandstone. — Tlils formatiou, like the Lower Heiderberg, is con- 

 spicuous in eastern New York, but thins out and disappears before reaching 

 the western part of the State. Although its geographical distribution is 

 about the same as the Lower Heiderberg, its fauna and flora are very 

 different, being pronouncedly Devonian. 



The Sylvania sandstone of northwestern Ohio, which was at first 

 referred to the Oriskany, was finally considered by Orton, on paleonto- 

 logical grounds, to be a part of the underlying formation, and therefore of 

 Upper Silurian instead of Devonian age. 



corniferous limestone. — The rocks of the Comiferous epoch in New York 

 include the Schoharie and Caudagalli grits as well as the Corniferous lime- 

 stone; but only the limestone appears in western New York. It outcrops 

 in a narrow strip leading eastward from Buffalo to the Hudson River. This 

 limestone, being a more resistant rock in western New York than the forma- 

 tions immediately above and below, now presents a well-defined escarp- 

 ment, over which several small streams have waterfalls. Hall divided it 

 between the Onondaga and Corniferous, the former including the gray 

 lower member and the latter the darker-colored upper inember of the 

 formation;^ but the earlier classification by Eaton has now become estab- 

 lished. The thickness of this formation in New York is commonly only 

 100 to 150 feet, but in the eastern part of the State it in places reaches 

 about 250 feet. 



1 New York Geol. Survey, Fourth Geol. District, 1843, pp. 151-176. 



