208 A POPULAR EXPOSITION OF THE 
been manufactured from a dark dolomitic bed of this age, occurring 
on the Magdalen River, in Gaspé. 
Middle Silurian Series. The rocks of this series, as explained on a 
preceding page, originally formed part of the Upper Silurian division. 
They have been separated from the latter, by the officers of the 
- Canadian Geological Survey, in consequence of certain peculiarities 
connected with their occurence in the Island of Anticosti. In this 
island, situated at the entrance of the St. Lawrence Gulf, the rocks in 
question contain fossils belongmg to both the Lower and Upper 
Silurians (as occurring elsewhere), and thus appear to offer a tradi- 
tional series, or middle term, between these two divisions.* They 
compose the “ Anticosti group” of Sir W. E. Logan, with the over- 
lying Guelph deposits ; and present, in ascending order, the following 
formations :—(1.) The Medina and Clinton Formation; (2.) The 
Niagara Formation; and (3.) The Guelph Formation. These, as 
regards Western Canada, might fairly be grouped together, under the 
term of the Magara Group. 
Medina and Clinton Formation.—In the State of New York, the 
rocks of this subdivision constitute two more or less distinct sets of 
strata ; but in Canada, the upper or Clinton series merges on the one 
hand into the underlying Medina beds, and, on the other, into the 
succeeding Niagara series. Its deposits consequently are partitioned 
off between these two formations, the term “Clinton” being, how- 
ever, retained to designate the higher strata of the first or lowermost 
of these. Thus defined, the Medina and Clinton subdivision consists 
in Canada of red and green arenaceous shales, succeeded by a coarse 
and somewhat loosely consolidated sandstone of a red colour, with 
overlying soft red marls and shaly beds, striped and spotted with 
green, and capped by a bed of grey sandstone (known as the “grey 
band,”’) of from ten to twenty feet in thickness. These strata, about 
614 feet m thickness at the western extremity of Lake Ontario, con- 
stitute the Medina series proper. The succeeding Clinton beds 
comprise a series of green, greyish, and red shales—the latter, highly 
ferruginous—with some interstratified limestones and dolomites. At 
the mouth of the Niagara River, the Clinton division, as thus defined, 
is merely a few feet thick; but it increases in thickness towards the 
north-west, and attains to about 180 feet on the shores of Georgian 
Bay, by Cabot’s Head. 
* The same holds good however, to some extent, in other localities. 
