680 
DESCRIPTION OF PLATES. 
PLATE XIII. 
Section 1. Natural section along the Genesee river, from Mount-Morris to Portage, showing the Genesee 
slate succeeded by the rocks of the Portage group. 
Section 2. Natural section along the Cattaraugus creek, exhibiting rocks of the Portage group. 
Section 3. Section across the formations from Cleveland, on Lake Erie, to the Mississippi river. 
This section commences with rocks of the Portage group, and shows the succession of the Che. 
mung group, the Conglomerate and the Coal measures. Descending to the southwest, we pass over 
the same formations, which are underlaid by a black slate, resting on the Corniferous limestone of 
New-York. The Corniferous and Onondaga limostones are well represented; and below these we 
find a drab-colored soft limestone, which is followed by a continuation of the Niagara limestone. 
Below this we find impure arenaceous limestone, and thin-bedded limestone and shale, which show, 
by the contained fossils, their equivalency with the Hudson-river group of New-York. Following 
the section from Cincinnati southwesterly, very nearly the same order among the strata is observed, 
with the exception that the Chemung group is separated from the Conglomerate by a yellowish 
grey sandstone, with thin beds of oolitic limestone, and above this by thick-bedded grey limestone, 
which increasing westward forms the most important limestone formation of the Mississippi valley. 
This limestone is followed by the Conglomerate and the great Illinois coal-field. 
Section 4. Section across the State of New-York from northeast to southwest, showing the natural order 
of succession among the strata, from the Primary upwards to the Conglomerate of the Carboniferous 
System. By uniting this section with the one above it, we have an almost continuous section from 
the northeastern part of New-York to the Mississippi river. In the space between Chautauque 
county, the termination of this section, and the commencement of the other at Cleveland, there are 
no rocks seen, except those of the Portage group. 
PLATE XIV. 
Surface of limestone, exhibiting furrows and striae, a , c, e,f g and h are nodules of hornstone. At a, 
c and g, these have resisted the wearing force, and are elevated above the general surface. At e, f 
and h the nodules have been broken off, so that their surface is now lower than the surface of the 
surrounding stone. From a to b, and from c to d, there is a little elevated ridge of stone remaining, 
which has been protected from wearing down by the hornstone before it. It will be perceived that 
the striae are often convergent or divergent, and that near the bottom of the plate there are two 
which are curved and suddenly terminate. 
PLATE XV. 
View from Bigflats, looking down Chemung river. The hill on the south exhibits numerous gorges, 
or incipient ravines, which are annually deepened by the action of frost and water. 
