224 



Report of the State Geologist. 



The exposure of these rocks in the gorge of the Genesee river from Mt. 

 Morris to Portageville, from which the group derives its distinctive appellation, 

 is but a comparatively short distance from the salt wells in the southern part 

 of both the Genesee and Oatka valleys, and a description of the rock section 

 there will apply to the whole of the western part of the district. 



As previously stated, the dam at Mt. Morris is built upon the Styliola 

 limestone. 



Above it, and exposed on both sides at the mouth of the gorge, are the 

 blue-black upper Genesee shales capped by a bed of densely black and 

 bituminous non-fossiliferous shales, the whole mass having a thickness of 

 about 100 feet. 



The top of these black shales come down to the water level a mile or two 

 up the river, and above them is exposed a band of soft clayey bluish-grey and 

 olive shales 150 feet thick, in which there are no sandstone layers, but rows 

 of flattened, impurely calcareous concretions that weather to a yellowish brown, 

 appear at intervals of from two to five feet. 



This grey band is uniform in character from top to bottom, and the upper 

 and lower limits are plainly marked by the contrast of its light color with the 

 black slates above and below. It is abundantly exposed near the Craig 

 Colony (Son Yea), five miles east of Mt. Morris, along Cashaqua creek, and 

 was hence termed by Professor Hall the Cashaqua shales. 



The thickness of the grey band diminishes gradually toward the west, 

 On lake Erie, at North Evans, it is thirty-two feet. It is exposed in the 

 mouth of the small creek in the village of Wyoming and about the mouth of 

 the old Globe Salt well, and also in the bed of the creek one mile south of 

 Wyoming on the east side of the valley. 



Overlying the Cashaqua beds is a band of black shale about twenty-five 

 feet thick which is succeeded again by a mass of dark blue and black shales^ 

 with which thin sandstones or flags are abundantly interstratified, the whole 

 being about 000 feet thick, and known as the Gardeau flags. 



In the lower half of these beds the shales are very dark, and thick beds 

 of black slates occur at frequent intervals, Avhile the flags are few and thin, 

 but toward the top, the shales are mostly light bluish-grey or olive and the 

 sandy Layers but a few inches apart. 



The dark beds arc exposed in the vertical cliffs and escarpments along 

 the Genesee river from Gibsonville to near the foot of the lower Portage 

 falls, and the upper division from the latter point to the top of the upper 

 falls. 



