190 A POPULAR EXPOSITION OF THE 
Potsdam, near Ogdensburg, in the State of New York. This name 
was applied to it by the New York geclogists, long before the Geolo- 
gical Survey of Canada was commenced. 
The Calciferous Group :—This division was formerly known as the 
Calciferous Sand, Rock formation, a name bestowed upon it by the 
New York Survey. The latter term, however, is to some extent a 
misnomer, since the prevailing or more characteristic strata (in the 
unaltered districts) are chiefly dolomitic limestones ; although many 
contain, it is true, a considerable amount of sandy or silicious matter. 
A specimen from Rigaud gave to Prof. Hunt an amount of insoluble 
matter equal to 36:90 per cent.; and samples from near Prescott, 
and from the Beauharnois Canal (the latter containing casts of 
Ophileta compacta) yielded to the writer amounts varying from 
27°12 to.over 4U percent. Other specimens from near Brockville and 
elsewhere, left, however, an insoluble residuum of less than 8 per cent. 
The rocks of this group may be conveniently discussed under 
three heads, viz.:—Normal Deposits; Displaced and Altered strata 
of Eastern Canada; and Altered strata of Lake Superior. 
Normal deposits of the Calciferous Group :—In Canada these con- 
sist principally of dark-grey dolomitic or magnesian limestones, many 
containing, as stated above, a certain amount of arenaceous matter. 
They are also interstratified very frequently with beds of grey, white, 
or brownish sandstone, varying in thickness from a few inches to 
four or five feet. The calcareous beds in many districts yield but a 
poor description of lime, and hence the term “ bastard limestones,” 
often applied to them by settlers and others: Small cavities lined 
or filled with cale spar, or more rarely with quartz, heavy spar, or 
gypsum, occur in some of the beds; and these and other beds occa- 
sionally exhibit in places a coarse concretionary structure. Fossils 
are of rare occurrence. The most common, perhaps, is the Ophileta 
compacta, fig. 158. Scolithus 
casts (figured on an earlier 
page) appear also in certain 
strata. In Western Canada, 
these normal Oalciferous rocks 
are apparently unknown west of 
the gneissoid belt that crosses 
the St. Lawrence at the Thou- 
sand Isles. They ET) AOE Fig, 158.— Ophileta compacta (Salter) 
however, in a thin band along 
