1084 NEW YORK STATE MUSEUM 



The portion of this section which corresponds to that in the 

 canal cut, is seen to show some differences. However, the rapid 

 changes in character of the superposed beds may be taken as 

 a good indication of the limited lateral extent of most of them. 



The red shale appearing in the upper part of this sec- 

 tion is the same as that exposed in the upper part of the canal 

 cut. At Pittsford, 2 miles southeast of this cut, the canal is 

 excavated through red shale mottled with green. At Carters- 

 ville, 2 miles farther southeast, this same rock occurs in the 

 canal bed and 40 feet lower in the waste weir. At Fairport, 

 4 miles northeast of this, it is again exposed in the canal, and 

 by well-borings is shown to have a considerable thickness at 

 that place. 



It thus appears that this red shale corresponds to the lowest 

 division of the Salina recognized in western New York by Hall, 

 and immediately overlies the stratum containing the fauna 

 herein described. 



A few important facts relative to the physical changes attend- 

 ing the introduction of the Salina fauna into the area are 

 well illustrated by these sections. The exposures on the west 

 branch of Allen creek, from which the lower part of this sec- 

 tion was taken, show in the upper portion a progressive change 

 of conditions: first, from those of the Niagara sea, in which 

 stromatoporid reefs were widespread and an incipient Guelph 

 fauna nourished, to those under which thin layered, impure, 

 ripple-marked dolomite was deposited and fucoids appear to 

 have been the only forms that abounded; then, to conditions 

 for the formation of a tough, porous, very bituminous lime- 

 stone, succeeded by a phase during which a stratum of thin- 

 layered, bituminous accretionary limestone, forming flat, imbri- 

 cating, shell-like domes, 1 was deposited; and, finally, to condi- 



1 This rock is the same as that south of Lockport, Niagara co. noted by Hall, 

 Geol. N. Y. 4th Dist. p. 92, r and also exposed in the southern part of the city 

 of Niagara Falls. It is probably identical with that described by Vanuxem 

 in the Geol. N. Y. 3d Dist. p. 91, as a limestone, small in quantity and in hem- 

 ispheric concretions, whose parts are more or less concentric to each other like 

 the coats of an onion, and regarded by him as an attenuation of the Lockport 

 dolomite. 



