29 



oxidize along these, where water and oxygen find a ready 

 access. Nodules of pyrite, often of quite large size, are com- 

 mon in this shale. 



The gray Genesee shales, being calcareous, weather more 

 readily than the black, which, from the absence of soluble 

 material offer peculiar resistance to the chemical action of 

 the atmosphere. Hence the portion of the cliff formed by 

 the lower Genesee shales recedes rapidly through weathering, 

 while that portion formed by the upper black Genesee shales 

 recedes only by the fall of the undermined portions. 



The Styliolina limestone appears in the bank seventeen 

 feet above the top of the falls. It has an average thickness 

 of six or seven inches, and in character does not vary much 

 from the outcrops in other sections. It frequently projects 

 beyond the underlying shales, while blocks which have fallen 

 to the base of the cliff are not uncommon. 



The whole of the Moscow shales are exposed in this sec- 

 tion, lying between the Styliolina limestone above, and the 

 Encrinal limestone below. Their thickness is nearly seven- 

 teen feet, and they usually form an almost perpendicular 

 wall. A smooth face occasionally appears where a joint 

 crack has cut the rock in the direction of the face of the 

 section. This feature, however, is not characteristic, the 

 calcareous shales, probably from their more tenacious 

 nature, being much less fissured than the bituminous shales. 



Five inches below the Styliolina limestone is a layer of 

 concretionary limestone, gray, compact and practically 

 non fossiliferous. This apparently corresponds to the layer 

 of concretions noted in a similar position in the preceding 

 sections. A few layers of scattered concretions appear in 

 the shale below this concretionary limestone. 



The most interesting portion ot these shales is the "coral 

 layer " of the Spirifer consobrinus fauna. This layer appears 

 in the bank eighteen or twenty inches above the Encrinal 

 limestone, and can be traced the whole length of the section. 



