On the Silurian System of the Lake Superior Region. 183 
The thin and even-bedded layers at the mouth of the river, 
may be quarried to a considerable extent, whenever there shall 
exist a demand for them, and they will form a durable building 
material. ‘Ihe succeeding layers are too irregular to be of any 
value, except for burning into lime. 
t the lower mill-dam, a mile above the first exposure, the 
banks of the stream, as well as the base of a small island, consist 
of beds of limestone, which form an escarpment fifteen feet thick. 
These also belong to the Trenton group, as indicated by the fol- 
lowing fossils, which were collected at this point: Isotelus gigas, 
Calymene Blumenbachii, var. senaria, Orthis testudinaria, Lep- 
lena sericea, and L. alternata. : 
fascending the river, this limestone, and even the identical 
beds, continue as far as the Lower falls, distant two miles from 
the upper mill-dam. ‘The stream for the most part is very rapid, 
and the dip of the strata very nearly corresponds with the descent. 
ble iMterest, noticed here for the first time. These compact, grey 
beds lie above the limestone seen at the Lower falls, since they 
clearly pass beneath the channel of the river, before the others 
ge. Between the Lower falls and the Meadow,* distant 
e f 
wit ent size, the nearest ones standing out in bold relief, while the farthest blend 
the forest growth of maples, 2 &c. Their mode of growth shows that, 
