556 



Revieivs — Canadian Geology- 



commonly possess the pillow or ellipsoidal structure which has now 

 been recognized in so many different parts of the world. A very 

 useful hibliographj' and discussion of the origin of pillow lavas is 

 given, and the author comes to the conclusion tliat, as elsewhere, the 

 strijcture is to be attributed to extrusion under water. By contact 

 metamorphism due to Inter batholithic intrusion the more basic rocks 

 have been transformed into hornblende schists and amphibolites, and 

 the more acid types into sericite schists. In the southern part of 

 the area, the Abitibi group is represented by sediments more or less 

 metamorphosed. They are distinguished as the Pontiac series, their 

 strati graphical position relative to the volcanics being still unsettled. 



Into the Abitibi rocks granitic batholiths are intrusive. Locally 

 the granite passes into diorite, and where the rock is rich in horn- 

 blende the change of composition can often be traced to the 

 assimilation of basic volcanic rocks. To quote the author: "There 

 appears to be complete gradation from blocks of rocks (xenoliths) 

 which undoubtedly belong to the Abitibi group to hornblende 

 granite." The intrusions made room for themselves by lifting and 

 thrusting aside the surrounding rocks and by sub-crustal stoping, but 

 the relative importance of these three methods are, unfortunately, 

 not discussed. 



Lying unconformably on the denuded surface of the rocks already 

 described is a group of clastic sediments which constitute the Cobalt 

 series. At the base of the series and often at the summit con- 

 glomerates are found. Their possible modes of origin are thoroughly 

 discussed, and the evidence (undecomposed and angular character of 

 the pebbles and the abundance of ' soled ' and scratched examples) is 

 held to point to a glacial origin. The intermediate beds are of 

 lacustrine origin and seem to represent an interglacial episode. The 

 whole series is classed as Huronian, no more detailed correlation 

 being possible. ^ 



Of probably later date than the Cobalt series are a large number of 

 diabase dykes and an isolated and unique intrusion of syenite porphyry. 



The author describes the mantle of glacial and post-glacial 

 (lacustrine) deposits, and concludes with some account of the ore 

 deposits and economic possibilities of the district. The outstanding 

 features in the geological history of the region appear to have been — 

 (1) The stupendous vulcanism of its early history. (2) The 

 undisturbed continental character of the region, interrupted only by 

 a short period of marine submergence in Silurian time. (3) The 

 occurrence of two prolonged eras of denudation, terminated in each 

 case (Huronian and Quaternary) by continental glaciation. 



Arthur Holmes. 



V. — The Aech^an Geology of IIaint Lake Re-studied. By 

 Andrew C. Laavson. Canada, Department of Mines, Geological 

 Survey Memoir 40. pp. vii + 115 and map. 1913. 



IN 1887 Dr. A. C. Lawson described the pre- Cambrian geology of 

 the Rainy Lake region of North-Western Ontario in a memoir 

 which has since become classic. In it he described two series of 



