MINERALS AND GEOLOGY OF CANADA. 19] 
the inner or south-western edge of the outcrop of the Potsdam 
series in the Townships of Pittsburg and Loughborough, although 
no certain indications of their presence have as yet been found. 
On the eastern side of the gneissoid belt, they are somewhat exten- 
sively developed—as shewn by the area marked 4 in the map a few 
pages further on (fig. 249)—although more or less obscured by thick 
beds of Drift. Exposures occur in the Counties of Leeds, Gren- 
ville, Lanark, Renfrew, Carleton, &c., of this district. An impor 
tant vein of lead ore (galena) occurs in this Formation in the Town- 
ship of Ramsay, Lanark County. In Eastern Canada, these beds 
occupy also a considerable area, and occur in the Counties of Beau- 
harnois, Vaudreuil, Two Mountains, Chambly, L’ Assomption, &e. 
They have been discovered likewise, of late years, in the Mingan 
Islands and on the adjacent coast, a locality in which they have 
proved more fossiliferous than in other and more western sites. 
Displaced and altered Calciferous Rocks :—The displaced strata 
and altered beds of this age in Eastern Canada, are known more espe- 
cially as the Quebec group. Under this term, however, the succeeding 
Chazy beds (in an equally altered condition, and which cannot in this 
district be well separated from the Calciferous deposits) are also inclu- 
ded. ‘These strata, until a comparatively recent period, were thought 
to occupy a somewhat higher place in the Silurian series, or to lie 
at about the horizon of the Hudson River Formation, near the top of 
the Lower Silurians. The fossil evidence traced out by the skill and 
perseverance of Mr. Billings, Palzeontologist to the Geological Survey 
of Canada, first shewed their true position. They consist of a series 
of grey, black, red, and green shales, in places over a thousand feet 
in thickness, with interstratified beds of dark and other coloured 
dolomites, limestones, and sandstones, holding graptolites, brachio- 
pods, trilobites, and other fossils. In this condition, these beds occur 
Fig. 160. 
a, Phyllograptus typus (Hall). 
6. Obolella pretiosa (Billings). 
Fig. 159. ce. Lingula Quebecensis (Billings). 
Graptolithus Logani (Hall). 
