494 
GEOLOGY OF THE FOURTH DISTRICT. 
perpendicular bluffs from ten to one hundred feet in height. Green shale alternates with the 
thicker courses of black, and beyond this the black shale increases in proportion as far as 
Portland harbor. Both green and black shale contain septaria, and more rarely, thin sandy 
layers, which are so numerous in the Portage group, constituting the flagstones further east. 
From Portland harbor to the State line we have similar slaty and crumbling shales, alternating 
with thick and thin courses of sandstone, all possessing a similar general character. Arriving 
at the State line, we are able to trace the same group in the deep ravines for two or three 
hundred feet higher before there is any marked change. Throughout the whole extent there 
are scarcely any fossils except fucoids, and these abound wherever the thin sandy layers 
occur. 
All the northern part of the county below the elevation of fourteen hundred feet above tide 
water, or about eight hundred and forty feet above Lake Erie, is underlaid by the shale and 
thin sandstone of the group above mentioned. These rocks are distinguished from those 
above by the almost entire absence of all fossils except fucoids, as well as the greater pre¬ 
dominance of shale. In the southern part of the county the rocks of this group are not seen, 
having passed below the level of the lowest valleys. 
All the southern part, as well as the higher portions of the northern part, are occupied by 
the Chemung group, readily known by the great number of shells of the genera Strophomena, 
Orthis, Delthyris, Avicula, <j~c. which characterize it every where. In this group the pro¬ 
portion of sand increases over that below, and in its upper part the larger proportion is sand¬ 
stone. 
The rocks of this group can be seen to great advantage in the Chautauque creek, six miles 
above Westfield, and in the outlet of Chautauque lake below Jamestown. They can also be 
examined to some extent above Rice’s mill on the Twenty-mile creek, and in many of the 
ravines along the Conewango and Cassadaga valleys. The strata are no where seen except 
in ravines or the banks of streams. 
The extreme southern part of the county is comparatively low, rising to less elevation than 
the middle portions. 
Many of the hills are capped with conglomerate, which is the highest rock in the county. 
From the portions remaining, the rock appears to have been originally of variable thickness; 
in some places not more than five or six feet, and in others fifty or sixty feet. Where the rock 
is free from pebbles, it is known by being more friable than any of the sandstones below ; and 
also by the lines of deposition being at varying angles, as if acted upon by currents from diffe¬ 
rent directions. In such cases it forms a good building or underpinning stone, easily dressed, 
and readily obtained in blocks of large dimensions. It is, in fact, almost the only stone in the 
southern part of the county which can be obtained more than a few inches in thickness. 
The principal places where it is quarried are, upon the top of a hill about two miles from 
Ashville; another quarry four miles north of Panama, and again one mile northwest of this. 
From these places, considerable quantities of the rock have been taken. It is associated with 
a few inches of the coarse conglomerate. 
On the north side of Chautauque lake, it occurs on the land of Mr. Young; also on the 
