152 Review of the New York Geological Reports. 



lake Ontario and the northeast corner of lake Erie ; except near 

 its eastern termination, where it first expands between the east- 

 ern shore of lake Ontario and Fish Creek, and then inclining a 

 little southerly, rapidly tapers off to a point, and vanishes near 

 Schoharie. 



South of the latter, and parallel to it, is the Helderberg divis- 

 ion, occupying a narrower but longer strip of country; for near 

 Schoharie, it sweeps off in a curved line towards the south, along 

 the Helderberg range, parallel with the Hudson river, as far down 

 as Kingston, and thence southwest to the great bend of the Del- 

 aware, where the Jersey's northern State line strikes that stream. 



The fourth, or Erie division, has a superficial area about equal 

 to that of the other three put together. Running west and east, 

 it stretches nearly across the State, covering the country between 

 the Pennsylvania line and the south boundary of the Helderberg 

 division ; i. e. the southern third of the State of New York. 



In the eastern portion of this tract, the Erie division is covered 

 by the sandstones of the Catskill. 



Each of the four divisions embraces the following rocks, be- 

 ginning with the lowest : 



Champlain division. — Potsdam sandstone, calciferous sand- 

 rock, Chazy and birdseye limestone, marble of Isle La Motte, 

 Trenton limestone, Utica slate, Loraine shales, grey sandstone, 

 conglomerate. 



Ontario division. — Medina sandstone, green shales, and oolitic 

 iron ore, Niagara limestone, red shale, Onondaga salt and plaster 

 rocks, Manlius water-lime. 



Helderberg division. — Pentamerus limestone, Delthyris shale 

 limestone, Oriskany sandstone, Encrinital limestone, Caudigalli 

 grit, Schoharie grit, Helderberg limestone. 



Erie division. — Marcellus and Hamilton shales, Tully lime- 

 stone, Genesee slate, Ithaca and Chemung shales and grits. 



Without at present attempting a detailed description of the in- 

 dividual members, let us review them as a whole. 



The lithological character of the Champlain group is sili- 

 ceous at the base ; gradually acquiring calcareous matter as it in- 

 creases in thickness, it becomes a pure limestone rock; then we 

 have an intermixture of argillaceous sediment, which increases 

 in quantity, until the calcareous particles give place to a dark 

 colored clay or mud, in the form of shale ; the argillaceous beds 



