REVIEWS QI 
are, for example, seven Cretaceous formations, each bounded above and 
below by an unconformity. Much the same may be said of the later 
formations. The Cretaceous strata of the region have a total thickness 
of 720 feet, the Eocene, 160 feet, the Miocene, 100 feet, the Pliocene (?), 
40 feet, and the Pleistocene about 100 feet. 
R. D.S. 
Onaping Map-Area. By W. H. Coxiins. Ottawa: Canadian 
Geological Survey, Memoir 95, 1917. Pp. viiit157, pls. 11, 
figs. 8, map. 
A very concise report on the geology of an area of approximately 
3,500 square miles the center of which is 50 miles north of Sudbury. 
The area lies within the southern part of the pre-cambrian shield and 
its topography is that of a hummocky plateau 875 to 1,450 feet above 
the sea. The most important physiographic features antedate glacia- 
tion. ‘The two intersecting series of parallel lake basins, in the south- 
west quarter of the area, probably follow faults. 
The solid rocks, all pre-Cambrian, are separable by a great uncon- 
formity into a pre-Huronian group and a Huronian group. The pre- 
Huronian consists of a schist-complex and intrusive granite-gneisses. 
The schist-complex consists of volcanics and subordinately of water- 
deposited tuffs, iron-formation, and other sediments. ‘The structure of 
this schist-complex, wherever determinable, is that of low anticlinoria 
and synclinoria. Dynamic metamorphism has converted the original 
volcanics and sediments into chlorite and sericite or paragonite schists. 
Near the granite-gneiss batholiths the effects of contact metamorphism 
are very marked. This schist-complex represents a period of extensive 
vulcanism and the formation of shallow-water or land deposits. The 
intrusive granite-gneiss series is dominantly granodiorites with which 
are associated a great variety of amphibolites, diorites, aplites, pegma- 
tites, and other types. ‘The diversity of types is explained by primary 
differences in the intruding magma, magmatic differentiation, and large- 
scale magmatic assimilation of older rocks. Crenulated interlocking 
contacts of larger mineral individuals with irregular shape and orienta- 
tion are textural features very characteristic of these assimilated prod- 
ucts. Good photomicrographs are shown to illustrate these features. 
In the future these criteria may prove of great assistance in determining 
this obscure type of metamorphic rocks. 
The Huronian rocks constitute the Cobalt series, divisible into 
two parts. The lower part (Gowganda formation, o-3,000 feet thick) 
