REVIEWS 485 
siderable attention. This memoir describes in some detail one of these 
areas of basic pre-Cambrian rocks and is representative of the geology 
of the mining camps of northern Manitoba. 
The area lies along the border of the Laurentian Plateau to the 
north and the Great Plains to the west. The average elevation of the 
Laurentian Plateau part is about 950 feet above sea-level, the highest hill 
being 1,060 feet and the lowest flat 818 feet above sea-level. This 
hummocky surface of low relief represents the surface of a pre-Ordovician 
peneplain recently uncovered and slightly modified by Pleistocene 
glaciation. The streams are characterized by lake expansions, rapids, 
and waterfalls. Lakes with irregular outlines and many islands are 
abundant. 
The rocks fall into four groups: (1) Pleistocene drift and stratified 
clay; (2) Ordovician dolomite; (3) pre-Cambrian granite and its 
differentiates; and (4) pregranitic complex of igneous and sedimentary 
rocks. 
The Pleistocene deposits consist of drift, outwash material, and 
stratified clays deposited in glacial Lake Agassiz. The Ordovician 
dolomite forms an irregular escarpment across the southern border of 
the area. No clastic base is present and the Ordovician seas advanced 
over a slightly rolling surface. A few fossils of Trenton age have been 
found in this dolomite. The pre-Cambrian granites, the most abundant 
rocks of the area, are intruded as stocks and batholiths and vary con- 
‘siderably from place to place in both mineralogical and chemical composi- 
tion. Massive reddish biotite or hornblende-biotite-granite is the most 
abundant type. In general these granites are massive, but in places 
gneissoid types occur. Pegmatite dikes and quartz veins represent the 
last phases of the intrusion. The pregranitic complex, the oldest 
rocks of the region, is divided into the Kiski volcanics and the Wekusko 
sedimentary series. The Kiski consists largely of volcanic rocks varying 
in composition from rhyolite to basalt. Beds of pyroclastics are found 
interbedded with the flows. These rocks are altered to sericite, horn- 
blende, biotite, and chlorite schists. The sedimentary division or 
Wekusko series consists chiefly of garnet gneiss and mica schist with 
many other varieties of metamorphic sediments in smaller amounts. 
The series is of great thickness, is highly folded, and intensely meta- 
morphosed. Except for a small area of slate, the series is coarse clastics 
which vary considerably in coarseness from place to place and with local 
conglomerate horizons. 
The chief ore deposits of the region are gold-bearing quartz veins 
associated with the granite intrusives and cutting all pre-Cambrian 
