154 Review of the New York Geological Reports. 



In an economical point of view, this is probably the most im- 

 portant division in the New York system, as furnishing all the 

 plaster, water-lime, and salt water of the State of New York ; 

 besides, it affords fine beds of oolitic and fossiliferous iron ores, 

 similar to that in Pennsylvania, which supplies much of the Ju- 

 niata iron. 



The most remarkable fossils in the Erie rocks are Goneatites, 

 Orbiculas, the curtain and retort-shaped Fucoides ; several spe- 

 cies of Delthyris with the hinge very much produced ; some 

 species of Atrypa and Orthis, more or less of an orbicular form ; 

 some peculiar Cypricardites, Avicula, Orthonata, Strophomena, 

 Orthocera ; a trilobite which has received the generic name Dip- 

 leura ; but the crustaceans seem to have been rare during the de- 

 position of these strata. Here we find the first vestiges of land 

 plants in the New York system; the Goneatites, too, have not 

 been found as yet any lower in the series. 



Interspersed in the bituminous shale at the base of this group, 

 some partial patches of coal occasionally occur ; but all the nu- 

 merous explorations in search of a regular seam in the vicinity of 

 these rocks, have ended in disappointment. The fact is, these 

 beds lie many hundred feet below the base of the true coal meas- 

 ures, and were deposited long previous to the period when the 

 circumstances favorable to the formation of coal existed. It does 

 not appear that tins division has yielded any valuable minerals: 

 some of its members afford, however, some tolerably good build- 

 ing materials. 



The representatives of the rocks of this group in the west, are 

 the black slate and fine sandstones of Scioto, in Ohio, of the 

 knobby region in Indiana and Kentucky, and the southwest part 

 of Illinois, and the strata in the high ground of middle Tennes- 

 see, and the iron region of the same district. 



The lower and upper beds of this group, appear to be absent 

 in the West, but some of the middle beds have been identified. 



If the specific determination of fossils is to be depended upon, 

 the inference seems to be that the lower part of the upper Silu- 

 rian system of England, represents the middle beds of the Onta- 

 rio division of New York. 



The Helderberg division is chiefly calcareous; limestone and 

 shaly limestone below, sandstone and grit in the middle, and 

 limestone above. The most remarkable fossil genera in these 



