54 NEW YORK STATE MUSEUM 



stantly presents the same features as on the Cashaqua but thins 

 down to 33 feet on the shores of Lake Erie. 



The passage from the Middlesex to the Cashaqua shale is through 

 several alternations of light and dark layers in a few feet above 

 which horizon the black layers are infrequent and thin. They 

 reappear toward the top and after a few alternations like those at 

 the base become the homogeneous mass of black shale constituting 

 the Rhinestreet black shale, the succeeding member of the Portage 

 group. Fossils are not abundant in any part of the Cashaqua 

 shale, but a few may be found in all of the lighter beds and in the 

 upper and more calcareous olive shales they are fairly common. 

 Some large cephalopods are finely preserved in flat concretions 

 20 to 40 feet below the top of the formation. 



Concretions usually a foot or more in diameter in a row at the 

 top of these shales in this section and further east have a layer of 

 calcareous matter i^/^ to 2 inches thick at the base composed of 

 fossils, sometimes in fine condition. 



This is approximately the horizon of the Parrish limestone, a 

 thin calcareous layer of concretionary structure, continuous from 

 Canandaigua lake valley to Seneca lake and a reliable datum point 

 in the stratigraphy of that region. 



The fauna of the Cashaqua shale is diverse and interesting. This 

 horizon is the normal seat of the peculiar fauna of the Portage 

 group, which is continued eastward without much variation but at 

 the west shows differences of composition [see Clarke, Naples 

 Fauna of Western New York]. 



In the general section the more common forms are: 



Manticoceras pattersoni (Hall) Pterochaenia fragilis (Hall) 



Probeloceras lutheri Clarke P. cashaqua Clarke 



Tornoceras uniangulare (Conrad) Honeoyea major Clarke 



Bactrites aciculum (Hall) Ontaria suborbicularis (Hall) 



Orthoceras pacator Hall O. accincta Clarke 



O. Ontario Clarke Buchiola retrostriata (v. Buck) 



O. filiosum Clarke Paracardium doris Hall 



Phragmostoma natator Hall Palaeoneilo petila Clarke 



Liinulicardium (Pinnopsis) acuti- Lingula ligea Hall 



rostrum Hall Aulopora annectens Clarke 



L. (Pinnopsis) ornatum Hall Melocrinus clarkei Williams 



The Cashaqua shale is exposed in the walls of the gorge from 

 near the mouth where the base is seen over the black beds for 6 

 miles to the north end of Smoky Hollow where the southwestern 

 dip brings it down to the river level. Opposite the lookout stations 

 along the " High Banks " where the cliffs are 300 to 350 feet high, 



