REVIEWS 



503 



lie in synclines, for reasons which the writer hopes to demonstrate in a 

 later paper. 



Most of the high-grade ores bear from 45 to 52 per cent of manganese, 

 but many otherwise good deposits bear too much phosphorous to justify 

 exploiting them. "Hand-picked" ore is the highest grade. The ore is 

 not used for chemical purposes, but is employed in various high- 

 manganese iron and steel products; it is also of importance in making 

 brown, gray, and speckled bricks, when mixed with clay. 



The manganese reserves probably amount to 250,000 tons of 40 

 per cent manganese. The deposits are covered to the south by younger 

 formations, and could probably not be extensively worked in that 

 direction anyway, since concentration and oxidation have not been 

 extensive under the heavy capping. 



C. H. B., Jr. 



Magnesite Deposits of Grenville District, Argenteuil County, Quebec. 

 By M. E. Wilson. Memoir 98, Canadian Geological Survey, 

 Ottawa, 191 7. Pp. 88, figs. 2, pis. 11, maps 3. 



This district is bordered by the Ottawa River on the south and is 

 about halfway between Ottawa and Montreal. The magnesite deposits 

 are about ten miles north of the Ottawa River. 



Chapter i gives information of general interest about magnesite, 

 its uses, foreign source of supply, other Canadian magnesite deposits, 

 and the history of magnesite mining in Grenville district. 



Chapter ii is a brief statement of the geology of the district. The 

 oldest rocks belong to the Grenville sedimentary series and are intruded 

 by pyroxene-rich gabbro, diorite, and syenite belonging to the Buckingham 

 series. These two series are intruded by batholithic masses of granite- 

 syenite gneiss. All these rocks are intensely metamorphosed and are Early 

 pre-Cambrian in age. These Early pre-Cambrian rocks are intruded by 

 diabase dikes and a stocklike mass of granite-syenite probably of Late pre- 

 Cambrian age. The Paleozoic is represented by the Potsdam, Beekman- 

 toan and Chazy formations named in ascending order. Glacial bowlder 

 clay and gravel and Champlain marine clay form an irregular mantle 

 over the bed-rock surface. 



Chapter iii gives a description of the magnesite deposits and their 

 origin. The magnesite is associated with serpentine, dolomite and other 

 minerals in the metamorphosed Grenville sediments and close to outcrops 

 of the pyroxenic rocks of the Buckingham series. The deposits are 

 lens-shaped and the material is banded, the banding being due to 



