On the Silurian System of the Lake Superior Region. 181 
Arr. XVII.—On the Silurian System of the Lake Superior Re- 
gion; by James Hatu.* 
Chazy, Birds-FEye, Black River, and Trenton Limestones.— 
These limestones are so intimately connected, one with another, 
in the Lake Superior district, and each is so thin, that no ad- 
vantage can be derived from treating them separately. It is true, 
however, that each can be recognized asa distinct member of the 
‘lower Silurian geries, and is characterized by fossils peculiar to 
itself, as has been shown in New York. Reduced as these forma- 
tious are in thickness, it will, nevertheless, be necessary to study 
them separately, and for the geologist, or collector, to preserve 
the fossils distinct. 
Commencing at the eastern limits of the district, these lime- 
stones are first seen upon the St. Mary’s river; but they are bet- 
ter exposed upon the eastern side of St. Joseph’s island, than upon 
the main land of the Michigan side. The sandstone, which is 
seen on Sugar island, plunges to the south, and passes beneath all 
these limestones, leaving, as far as observed, no trace of the cal- 
ciferous ; but an interval, covered by drift, occurs, where no rock 
is visible. In examiuing the shore of the island, the first rock 
seen, after the disappearance of the sandstone, is the Birds-eye 
limestone ; but, further to the eastward, near a projecting point, 
some layers of the Chazy make their appearance, having, tow- 
ards the bottom, an arenaceous character ; while higher up, they 
assume an argillo-calcareaus composition, and contain fossils char- 
acteristic of this member of the New York series. This jime- 
Stone is also seen to pass directly beneath other beds, which, by 
their peculiar character, may be recognized as the Birds-eye. The 
fossils of the Chazy do not pass above the limits of the Birds-eye ; 
ut the respective limits of the two members are as well defin 
as in any of their eastern localities. : 
The Birds-eye limestone is, for the most part, thin-bedded, the 
layers being separated by shaly matter, which rapidly wear away 
under the influence of the atmosphere and the water, while the 
tder parts are brittle and easily fractured. This limestone ap- 
Pears to be more fossiliferous here than in New York, and, in the 
Upper layers particularly, we found a great number of Orthoce- 
Tatites, 
The Black-river limestone, or beds which may be regarded as 
the equivalent, seems to be intimately incorporated with the 
— ye; so much so, that no line of demarcation could be de- 
* The following pages are cited from Chapters IX and X, of Messrs. Foster é& 
Whitney’ Reporte dn toa Laie Rapicior Region, Part 2, and are in continuation of 
part of the work from which we have cited on pages 11 to 
