92 REVIEWS 
is composed of conglomerates, greywackes characterized by incomplete 
weathering and imperfect sorting, and a few beds of limestone. By 
many geologists familiar with this general region this formation in part 
at least is thought to be of Glacial origin. The upper part of the series con- 
sists of quartzites (chiefly Lorrain quartzite). As compared with the pre- 
Huronian, the Cobalt series is little metamorphosed or folded. In most 
places the Gowganda formation grades up into the Lorrain quartzite, 
but at some localities there is evidence of an erosion unconformity 
between the two. This local unconformity may be the result of overlap 
and probably does not represent a great time-gap. 
Both the pre-Huronian and Huronian are intruded by dikes and 
sills, probably of Keweenawan age. Many different rock-types ranging 
from norites to aplites are represented and here again the field evidence 
and relationships make it clear that this diverse petrological variety is 
due in some cases to original differences in the composition of the magma, 
in others to assimilation of country rocks, or to magmatic differentiation. 
Calcite and the association of quartz, chalcopyrite, and silver-cobalt- 
nickel minerals, which constitute the silver-cobalt veins of the area, are 
believed to be among the subsidiary differentiates. Primary calcite is 
found sparingly in the diabase dikes and abundantly in the aplite dikes. 
In two cases the aplite dikes merge into calcite veins. These sills and 
dikes and all older rocks of the region are cut by porphyritic olivine 
diabase dikes. 
The numerous gold-quartz veins near West Shiningtree Lake are 
irregularly mineralized and the gold content'is low. In this general 
region the post-Cobalt diabases have gold-bearing quartz veins associated 
with them. ‘The gravels along the Vermillion river have been worked 
for placer gold, but they are rather lean. Small silver-cobalt veins 
occur at Gowganda. The future commercial importance of the several 
iron ranges of the area is very doubtful. 
JS We 
Contributions to the Mineralogy of Black Lake Area, Quebec. By 
EUGENE PoItTEvVIN and R.P.D. GRAHAM. Canadian Geological 
Survey, Mus. Bull) No, 27, 1915. Pp. 103, pls. c2;aneseaas 
A detailed study of the minerals of the chromite and asbestos pits 
in the Black Lake area, Megantic County, Quebec. This is a very 
productive area, in the serpentine belt of the eastern townships. The 
country rocks consist of a complex of igneous rocks, ranging from the most 
