ONONDAGA LIMESTONE. 175 



strata, or at least from eight to leu feet of the rock consist of two-thirds flint. At Cherry- 

 valley, and farther west, the flint is in palmated and nodular masses, but arranged in 

 strata : the interior of a flint nodule is often calcareous. It is the most cherty or flinty of 

 any rock in the New- York series, and hence was named by the late Mr. Eaton, Corniferous 

 limerock. 



Extent or area over which the Onondaga limestone is the surface rock. It forms a narrow 

 belt from the Hudson to Lake Erie. This belt is on the south side of the Erie canal. Its 

 northern edge, beginning at Leeds, four miles west of Catskill, runs northeast to New- 

 Scotland. It then sweeps round the northern terminus of the Helderberg range, but keeps 

 south of the Cherryvalley turnpike. Its course is west from Schoharie to Blackrock, 

 though it will be observed that the edge is rather convex to the north, in consequence of 

 denudation which has taken place in the central j>art of the State, in the region of the 

 smaller lakes, as Cayuga and Seneca. It passes through Onondaga, Cayuga, Genesee and 

 Erie counties. The belt in some places is five or six miles wide, but considerably less in 

 others (See the accompanying geological map, upon which its course may be traced, being 

 the southernmost blue belt) . In the Hudson valley, it appears in an outcropping edge, and 

 also in a belt, sweeping round the base of the Catskill mountains, and passing a little west 

 of the valley of the Rondout, or along the Warwarsing valley. It terminates, or passes 

 out of the State of New-York, into New-Jersey, at the bend of the Delaware river. 



Thickness. The whole thickness of the rock included under the name of the Onondaga 

 limestone, is not less or more than sixty or seventy feet at Clark's in New-Scotland. It is 

 not far from one hundred feet at Cherryvalley. At Leeds in Greene county, the whole 

 mass does not appear to exceed twenty-five or thirty feet. At Leroy, the dark and com- 

 pact part of the rock known as the Corniferous limestone, is seventy-one or -two feet, and 

 is accompanied by thin masses of gray and dark colored limestone and hornstone, some 

 of which is slaty. The amount of siliceous matter is large at Leroy. It then forms the 

 limestone terrace, which continues onw T ard to Blackrock. At the latter place, the calca- 

 reous and flinty portions are more or less blended, and the laminae are separated by a 

 dark colored shale. 



If the rock is divided, and the low r er mass treated as a distinct rock, it is found that it 

 varies greatly in thickness on its westward route to Blackrock : in some places, as at the 

 Helderherg and Cherry-valley, it is twenty-five or thirty feet thick ; while at others, it 

 is only three or four. Indeed the entire mass of the limestone is unstable as to thick- 

 ness ; and it may be said that, for a limestone, it is quite unsteady as to composition : in 

 some places, the hornstone or chert predominates ; in others, it is a pure limestone ; and 

 in others still it admits considerable shale into its composition, though it usually appears 

 between the layers. The hornstone also differs somewhat in its characters : in one place, 

 it is massive and in beds ; in others, it is in nodules or palmated masses. As a whole, 

 this hornstone belongs to the corniferous mass ; in fact, it. was owing to its great abundance 

 that this name was given it. The impropriety of the name appears, however, when it is 



