26 NEW YORK STATE MUSEUM 



milldam at Cowlesville, and below the bridge over Buffalo creek 

 at East Elma, and the entire section in the bed and sides of Caze- 

 novia creek for more than a mile. There are also many outcrops 

 in small ravines and roadside gutters. 



RHINESTSEET BLACK SHALE 



This formation, consisting of a heavy mass of black shale suc- 

 ceeding the light colored Cashaqua beds, is 90 to 100 feet thick on 

 the east line of these quadrangles and 150 feet on the west. With 

 one exception, the Dunkirk black shale, higher in the series, it is 

 the only Devonic formation that decreases in thickness toward the 

 east. It extends as far as the Keuka Lake valley on the east, where 

 outcrops show but 6 to 10 feet of the black shale, and to the shore 

 of Lake Erie in the town of Evans, where it is 185 feet thick. On 

 these quadrangles it includes a few thin bands of dark bluish gray 

 shale usually from 3 to 5 feet thick that -contain large symmetric 

 concretions and septaria, some of which attain a diameter of 3 to 

 6 feet. 



The black shales are quite barren of fossils, except plant remains, 

 fish remains and conodont teeth, all of which are very rare. In 

 the lighter shales obscure forms like those found in the Cashaqua 

 shales occur but are also rare. 



Exposures. Rhinestreet shale is the surface rock over a large 

 area and is exposed in numerous ravines, frequently at and above 

 cascades produced by its greater resistance to the erosive power 

 of the streams than the more argillaceous Cashaqua shale. The 

 larger exposures are along Tonawanda creek at Sierks ; in the 

 Tannery Brook ravines ; in the upper part of Murder Creek ravine, 

 along Cayuga creek at Folsomdale, Buffalo creek at Porterville and 

 along Cazenovia creek at Jewettville and the banks of the gorge 

 for 3 miles below. 



HATCH SHALES AND FLAGS 



In the Genesee River Gorge section the Rhinestreet shale is suc- 

 ceeded by about 150 feet of dark ferruginous and light blue shales 

 with frequent layers of thin sandstone and overlaid by a well- 

 defined sandstone. The black Rhinestreet shale and these beds were 

 included by Professor Hall in the Report on the Geology of the 

 Fourth District, 1842, in the formation designated '' Gardeau flags 

 and shales." but for reasons set forth in New York State Museum 

 Bulletins 63 and 118 they were separated and considered as units 

 in the Portage series and designated '' Hatch flags and shales '* 

 from their exposure at the base of Hatch hill at the head of the 



