104 



GENESEE FARMER. 



April, 



■ ^^ ..-^^jx. _ ^ 



VIEW OF THE UPPER FALLS AT ROCHESTER (Fig. 24.) 



organic matter. The Niagara shale, however, 

 is destitute of those spheroidical concretions, 

 which in the Hamilton group are more or less 

 common, and in many places abundant. The 

 only approacli to a concretionary form seen in 

 this shale, is in the increased thickness of some 

 layers of impure limestone ; and this appears 

 rather due to a greater development of corals or 

 other fossils, around which the mud accumulated 

 more freely than elsewhere. A few such ex- 

 amples may be seen in the banks of the C4en- 

 essee at Rochester. 



The lower part of this shale is mostly free 

 from calcareous bands ; while towards the middle 

 and in the upper part, we find numerous thin, 

 wedge-form or continuous layers of impure lime- 

 stone, mostly composed of corals and other fossils, 

 and their surfaces covered with the same, form- 

 ing beautiful and interesting specimens for the 

 cabinet. The perfect similarity of these with 

 specimens from Dudley in England, together 

 with the identity of many of the organic forms, 

 renders the conclusion unavoidable that the two 

 are formations of the same age. These layers 

 are from half an inch to two inches thick; and 

 from the decomposition and sinking down of the 

 shale, they are usually found broken into frag- 

 ments. One of the most striking features of this 

 rock, is the abundance of its fossils. Scarcely a 

 locality can be examined where they do not oc- 

 cur in great perfection. 



The higher beds are well developed in the 

 fall at Wolcott Village, and the lower part of the 

 formation can be examined by following down 

 the ravine for a mile. This is the most eastern 

 locality in the district where we find the rock 

 exposed. West of this point, throughout the 

 county, it is seen in all the small streams which 

 flow into the lake. 



At Rochester it forms nearly the whole height 

 of the upper fall, and the banks on either side of 

 the river for more than a mile below. This 

 place offers a fine exhibition of the rock, and is 

 one of the best localities in the State for a natural 



jexposure. The constant undermining of the 

 banks precipitates large masses to the bottom, 



; and their fossil contents are thus made accessible. 



i At this locality, its upper and lower limits are 

 both plainly seen. Above it passes gradually 

 into an impure limestone which forms the beds 



i of passage from the shale to the limestone above. 



' The fossils mostly disappear at this point, and few 

 are found in this part of the mass. Below it termi- 

 nates abruptly, resting directly on the calcareous 



jbeds forming the upper member of the oreceding 



i group. There is never any gradual passage 



J from the one to the other, and the peculiar fossils 

 of the shale do not appear till we ascend some 



■ distance above the limestone. Nevertheless it 



I is true that two or three of the common fossils of 

 this shale have been found in the limestone below, 

 and at the same time the greater number marking 

 the Clinton group terminate below that rock. It 

 may therefore remain a question, perhaps, 

 whether these calcareous beds should be included 

 in the Niagara group. Since, however, they 

 bear a close analogy to the lower limestone of 

 the Clinton group, and terminate above abruptly 

 without offering any marks of gradual passage to 

 the next higher group, I prefer for the present 

 to include them in the lower, thus presenting a 

 natural lithological assemblage. The presence 

 of a few fossils common to the limestone and 

 shale above would apply equally to all parts of 

 the preceding group, a few forms being common 

 to all parts of both. 



The precise arrangement at Rochester is as 

 follows : — The terminating calcareous beds of the 

 Clinton group consists of fifteen or twenty thin 

 courses, each separated by a layer of shale some- 

 times of equal thickness to the limestone, though 

 generally thinner. The shale separating the 

 lower courses is green like that below, but higher 

 it becomes of tlie same color and character as 

 that above. The interlaminated shale is in all 

 cases destitute of fossils. The shale is partially 

 exposed in several small streams, and in the 

 lower escarpment which extends westward from 



