182 On the Silurian System of the Lake Superior Region. 
Further to the south, the Trenton limestone was observed ex- 
tending in a low cliff, for some distance along the river, maintain 
ing, to a great extent, the characters by which it is distinguished 
in more eastern localities. Its higher portions are made up, in a 
great degree, of crinoidal remains, and it preserves the same char- 
acter as this portion of the series in the Mohawk and Black-river 
valleys. The whole mass is evidently much thinner than at any 
locality east of Lake Huron, and there is, also a larger proportion 
of shaly matter, not only between the layers, but incorporated in 
them. : 
In addition to the evidence derived from lithological characters, 
the fossil contents are of such a character, and so abundant, as to 
leave no doubt in this respect. The aspect not only of this mem- 
ber, but of the others, was such as to impress one with the belief 
that, though identical in agé and in composition, and a continua- 
tion of their eastern equivalents, they were deposited under cit 
cumstances less favorable to organic life, resulting from the na- 
ture of the materials deposited, or from varying conditions in the 
ocean. ‘The quantity of shaly.materials mingled with this lime- 
stone, and distributed in layers between the beds, would seem to 
indicate that a shallow and turbid state of the water prevailed 
during its deposition. 
he observations made by Messrs. Whittlesey and Desor, on 
the Manistee river, tend to confirm these views. 
On the Escanaba river, for more than seventy miles along ifs 
meanders, above its mouth, these limestones are almost constantly 
exposed, and present these features. The river, for the distance 
of a mile before it enters the lake, flows over limestone sfrata, 
which are nearly horizontal, or dip very slightly in the direction 
consequently, the strata are cut through and their edges expose 
to the thickness of only a few feet. The first rock met with, in 
ascending the stream, is a tough limestone, in thin layers, 
Birds-eye, and contains Orthoceratites and other fossils, charactet- 
istic of that member of the series, as well as of the Black-river 
limestone. The succeeding layers, which are well-exposed about 
a mile above this point, consist of thin, irregular, or wedge-shaped 
layers of light ash-colored limestone, verging to a dark-blue color, 
and contain many species of fossils, characteristic of the Trenton 
ination of these crinoidal fragments shows that they belong ‘to 
genera, and, perhaps, species, known in this series elsewhere: 
