HAMILTON GROUP. 155 



From the north of Levana, no rock could be seen on the shore, until south of Aurora ; 

 there the harder variety appears. It is between these two points that the shales of Skanea- 

 teles, of the Report of 1840, are placed, being the second observed mass in the ascending 

 series ; they are less fissile, more calcareous, fossils more numerous as to kinds and individuals, 

 than in the mass to the north of Levana. It is in this part that the Mucronated delthyris, 

 Bufo asaphus, Linear strophomena, Umbonated orthis, etc. first appear. 



The harder variety, on the lake to the south of Aurora, forms a bluff rising near the water's 

 edge to the height of twenty or more feet. Its color by exposure is of a brown olive, and is 

 similar to the greater part of the harder shale of this group, and known in the Reports under 

 the name of Olive and Ludlowville shales. The more common fossils observed at the bluff 

 were the Concentric atrypa, and those of the Skaneateles shales. These shales are of con- 

 siderable thickness upon the lake ; falling, rising and disappearing as the direction of the lake 

 changes, as will be explained under the head of TuUy limestone. They present numerous 

 bluffs, and are finally lost under the encrinal limestone below Ludlowville. It contains 

 numerous fossils, among which, besides those already enumerated as existing towards Aurora, 

 are the Concentric cypricardite (C. concentrica). Corded cypricardite (C. subtenta), Wrinkled 

 cypricardite (C. nigosa), Eggform inoceramus (I. oviformis), Keeled strophomena (S. cari- 

 nata). Undulated orthonata, with numerous others belonging to the group, a few of which only 

 have been named. 



As before mentioned, these shales extend to the encrinal limestone. This is a mass of 

 impure limestone, rather a tough rock, usually of a brownish color, from three to four feet in 

 thickness, and containing in most parts of its range along the lake, numerous fragments of 

 encrinal joints or disks of crinoids, whence the name. It contains other fossils, but none 

 with certainty noticed, which differed from those of the group. It makes its appearance in 

 going south, first in the ravines near Ogden's ferry, and along the lake shore to the south of 

 the creek at Ludlowville. It resists the action of the weather, and projects from the side- 

 hill and ravines, and forms the first falls in the ravines. This mass does not appear to extend 

 far east, not having with certainty been recognized beyond the borders of Cayuga lake. 

 South of Borodino, a ledge of encrinal hmestone crosses the road ; but it has the thickness 

 of the Tully limestone, and the Genesee slate rests upon it. 



In the fourth district, the encrinal limestone appears, from the account given of it by the 

 Geologist of that district, to be a persistent mass ; appearing at various points between Cayuga 

 lake and Lake Erie, at its line of outcrop. 



Above the encrinal limestone, are the Moscow shales of Mr. Hall. The color of this mass 

 is of a darker blue along the lake; it is composed of finer particles, and is also more calcareous. 

 It extends to the Tully limestone, which is the termination upwards of the group. It contains 

 numerous fossils in common with the parts below the encrinal limestone, and may contain 

 some which have only been found in this shale, but which I am not able with certainty 

 to designate. In the fourth district it would appear that there is a difference, and that diffe- 

 rence will be made known in its report. There are some fossils which certainly are more 

 abundant in these shales at Ludlowville than in those below, along the lake ; such as the 



