32 



GEOLOGY OF ERIE COUNTY 



pyrite is extremely hard and is a mass of casts of fossils which 

 have been replaced by the pyrite. Fossils from this layer at 

 other points have been the subject of a monograph by Frederick 

 B. Loomis. 



A 



B 



D 



C 



F. Houghton, Photo. 



Fig. 12. Section of cliff, Cazenovia creek, south of Springbrook. 



A. Genundewa limestone, overhanging. 



B. Concretions imbedded in black shale. 



C. Genesee black shale. 



D. Pyrite layer. 



E. Moscow shale. 



The pyritiferous shale, also, is filled with fossils all of 

 which have been replaced by the pyrite. 



ienesee 



Beds 



James Hall considered the Tully limestone a line of demarca- 

 tion. The fauna of the beds above the Tully differs radically 

 from that below it. Conditions favorable to the great profusion 

 of marine life which characterized the seas of the period during 

 which the Hamilton beds were laid down seem to have come to 

 an end with the deposition of the Tully limestone. The difference 

 is more marked in the western part of the state than in the 

 eastern where there is more or less mingling of the faunas of the 

 Hamilton and Genesee beds. 



