PORTAGE GROUP. 
227 
The mass at this place is a soft argillaceous rock of a green color, rapidly crumbling on 
exposure, and forming a tenacious clay. From the influence of atmospheric agency, it is very 
difficult to procure good specimens ; and fossils not being abundant, they might be easily over¬ 
looked. It is, however, marked by certain species of shells which have not been seen in any 
other rock, and these have been found to hold the same position over an extent of 150 miles. 
On the Cashaqua, and in other places in the same neighborhood, it contains some flattened 
concretions of impure limestone, and sometimes of sandstone, but of these it presents no con¬ 
tinuous layers. It is deeply excavated, presenting high and abruptly sloping banks, which 
project into the valley on one side and recede on the other, as the stream winds along its 
course below. In looking down the stream, as represented in the woodcut at the head of the 
page, the slopes of these cliffs are free from vegetation, while on the opposite side they are 
entirely covered, often with large trees. This effect is produced by the action of the meander¬ 
ing stream, which flows in its channel from one side of the gorge to the other, continually 
undermining the rock which crumbles down from above, thus constantly presenting a fresh 
surface. 
At the eastern extremity of the district, and on the shores of Seneca lake at Penn-Yan and 
other places, this rock consists of a green shale with thin flagstones, and interlaminated sandy 
shale. It contains the same fossils ; and holding the same position as on the Genesee, it can 
be regarded only as the same rock, the intercalation of sandy strata being due to its proxi¬ 
mity to the place of origin. Farther east it is not recognized as a shale at all, the mass con¬ 
sisting of thinly laminated shaly sandstone. At Penn-Yan it often manifests a concretionary 
structure, and the sandy strata are irrregular in thickness and continuance. 
On tracing it west of the Genesee, it constantly presents the same features as on the Casha¬ 
qua creek, though the lower part is occasionally dark colored, and separated from the Gene¬ 
see slate by a thin calcareous band. It is exposed in numerous streams and ravines, the most 
important of which are those in the hills bordering on Allen’s creek, Tonawanda creek, and the 
branches of Seneca and Cayuga creeks. It appears at the village of Wyoming, in Wyoming 
county, and in numerous other points in the same neighborhood. On ihe shore of Lake Erie 
its whole thickness is seen in the high perpendicular cliff, having thinned from 110 feet on 
the Genesee to 33 feet at Eighteen-mile creek. At this place it retains all the characters 
which are peculiar to it on the Genesee, having changed only in thickness. 
2. Gardeau Shale and Flagstones. 
Along the Genesee river, above the last described rock, we find a great development of 
green and black slaty and sandy shales, with thin layers of sandstone, which form beautiful 
and durable flagstones; these are quarried from the same situation in many places in the 
district. The rocks of this part of the group form high, almost perpendicular banks on the 
Genesee, only indented by the incipient ravines caused by slides and the action of running 
water. From their great exposure along the Gardeau reservation, that name was adopted in 
29* 
