On the Silurian System of the Lake Superior Region. 185 
tough, silicious and irregularly-shaped concretions, or segrega- 
tions, which stand out in relief, while the calcareous part wastes 
ay. 
At the Upper falls, the strata rise more rapidly to the north- 
ward, and though the ascent of the stream is considerable, yet, 
on arriving at the foot, the calciferous sandstone is exposed, form- 
ing the base of the escarpment over which the water is precipi- 
tated; while, above it, there are two layers which represent the 
Chazy and Birds-eye limestones and the lower part of the Tren- 
ton group. 
Here, the following séction is exposed in an ascending order. 
1. Birds-eye limestone, fine-grained and compact, of a bluish- 
drab color. 
2. Calcareous layers, of a grey color, with crinoidal joints and 
other fossils, —4 feet. 
- A heavy-bedded, variegated limestone, with much silicious 
matter, the surface weathering very unevenly,—2 feet. 
4. A thick, silico-calcareous bed, with fossils in the upper part, 
—« leet. 
5. Silico-caleareous layers at the foot of the falls, thin and 
even-bedded,—1 foot. : 
‘The whole exposure at the falls is about fifteen feet, and in 
the bank above, about ten feet more. The beds forming the top 
of the falls disappear below the river, near the point where In- 
lan creek comes in from the east. ‘The layers having the char- 
acter of the Birds-eye limestone disappear a short distance below, 
and are succeeded by thin beds containing an abundance of Or- 
this lestudinaria, Leptena sericea, and JL. alternata, with other 
fossils of the Trenton limestone, and have the same character as 
some of the layers about midway in this group, as developed in 
the Mohawk and Black river valleys, in New York. Above the 
falls, the low cliff of fossiliferous limestone continues for some 
distance, gradually declining to two or three feet in height above 
the river. The same changes take place, with the recurrence of 
Méstones, at a point some three miles above the falls, and con- 
tnuing thence up the stream for the distance of two miles above 
8 forks, 
tock and the descent of the river, is less than sixty feet. ‘There 
's, however, very little parallelism between the two; for, within 
Stcoxp Sznims, Vol. XVII, No. 50—March, 1854. 24 : 
