ERIE COUNTY. 473 
The only representative of the Tally limestone is a layer of argillaceous, often concretionary 
limestone, about three inches thick, succeeding the Moscow shale. 
The Genesee slate succeeds the Moscow shale, and is found near the limit of the county, 
on the Eleven-mile creek ; it appears also on Cayuga creek, lot 30, town of Wales ; again, 
at Hatch’s mill on the Seneca creek, Indian reservation; and also on Cazenovia creek, near 
Aurora, and is barely visible in many other places in the small streams. It every where pre¬ 
sents its usual character of black, slaty shale, and is every where marked by the presence of 
Avicula fragilis. Its first appearance on the lake shore is in a high bank, twelve miles from 
Buffalo, forming about six or eight feet of the upper part of the rock ; beyond this it is not 
seen till after passing Eighteen-mile creek, where its whole thickness is visible, lying between 
the Moscow and Cashaqua shales. It disappears beneath the lake, nearly two miles south¬ 
west of Eighteen-mile creek. 
In Erie county, the Cashaqua shale is seen in the Cayuga, Little Buffalo, Seneca and Ca¬ 
zenovia creeks ; also in the banks of Eighteen-mile creek, extending for two miles or more 
from the lake. Southwest of the mouth of Eighteen-mile creek it appears in the high bank } 
exhibiting its whole thickness. It is of a greenish color, embracing numerous courses of 
irregular, flattened concretions, consisting of clay and sand, with some carbonate of lime. 
These masses are the only representatives of the continuous layers of calcareous and argilla¬ 
ceous sandstone, which occur further east. This shale forms a very tenacious, clayey soil, 
as is well seen after ascending the hill beyond Eighteen-mile creek, where the soil is almost 
entirely formed from this rock. It disappears near Lay’s tavern, three miles southwest of 
Eighteen-mile creek. 
Above the Cashaqua, we find black and dark colored shales; and to these succeed alterna¬ 
tions of dark green and black shales, the green portions often predominating for miles, and 
the whole extending beyond the county line. These are all destitute of fossils, except occa¬ 
sional traces of fucoids. The higher part of this group may be seen in following up the 
Little Buffalo, Seneca, and Cazenovia creeks and their tributaries. The layers of sandstone 
are thin, and afford good flagging stones ; they are also used for other purposes. This group 
occupies all the lower portions of the hills and moderately elevated grounds in the southern 
part of the county. It can be seen to advantage at Griffin’s mills, three miles south of Aurora. 
Several of the thin layers of sandstone alternating with shale are seen in a small stream one 
mile east of Aurora. 
Several quarries are opened near Boston centre, where the flagging stones of this group 
are quarried. The slabs are from one to six inches thick, and separated by joints of eight feet 
by six broad ; some are fifteen or twenty feet in length. 
The rocks of the upper part of the Portage group occupy the highest grounds of the 
southern part of Erie county, frequently outcropping on the small streams and ravines. The 
sandstone of this group is thin, compared with the same farther east, and there are but few 
quarries opened. 
About two miles south of Aurora, the higher rocks of this group are quarried by Mr. Treat 
[Geol. 4th Dist.] 60 
