374 Oeneral Description of Lake Erie. 



described by him thus*: — It is a siliceous or calcareous grey 

 rock, with aluminous cement, either slaty or in blocks, and 

 abounding in iron pyrites and petrifactions ; the latter some- 

 times being composed of the former. He has named it " se- 

 condary pyritiferous rock." In Cayuga Lake, according to Mr. 

 Eaton, these strata contain numerous thin horizontal seams of 

 bituminous and sulphureous coal, embraced by narrow layers 

 of iron pyrites, (which last alone is found in Lake Erie ;) where- 

 ever these are exposed, the adjoining rock was more or less 

 covered with Epsom salts, copperas, and alum. 



*• This rock occurs on the north shore only of Lake Erie, 

 from its south-east corner in Hamburgh, eight miles from 

 Buffalo, with very little interruption, to Sturgeon Point. 

 It appears from the ** Travels of Engineer D. Thomas, that 

 the same rock borders the lake to Cattaranghus, and pro- 

 bably much farther/' — {Eaton, p. 143.) In fact, according 

 to Dr. Mitchell, of New York-j-, it exists at Presqu'isle, 

 90 miles from the foot of the lake. Mr. Eaton continues, 

 " We see but little of the shelly rock, rarely exceeding twelve 

 feet in height, until we come to within about three miles of 

 Eighteen-mile Creek. On both sides of this creek the rock 

 is very similar. The loose scaly slate occupies about 25 feet 

 of the lower part, and the ranges of square-faced blocks of 

 limestone occupy about the same number of feet above, fre- 

 quently interrupted by the slate." (Eaton, p. 143.) The slaty 

 part is remarkable for its finely preserved organic remains : 

 both kinds, however, contain a great and equal number. They 

 are terebratulae, favasites, turbinolie, milleporites, trilobites 

 encrinites, orthocense. (Eaton.) Mr. Leseur, of Philadelphia, 

 found in the compact portion of this limestone, near Eighteen- 

 mile Creek, a univalve, which he has erected into a new genus, 

 with two species. He describes them thus : — Genus Maclurite. 

 Shell discoidal, much depressed, unilocular ; spire not ele- 

 vated, flat ; umbilicus very large, with a groove formed by the 

 projection of the proceeding whorls ; not crenulated. 



Species I. M. magna. Shell obtusely carinated on the ex- 

 terior upper edge, whorls rapidly increasing in size ; aperture 



* Geological Survey of the District axjoining the Erie Canal, p. 38. 

 t Minerva of New Work, 1824. 



