CURRENT PRE-CAMBRIAN LITERA TURE 4 1 1 



where we have Archean and Algonkian gneisses and post-Algonkian 



gra While in different parts of the region the different conclusions 

 above outlined have been reached, for the Adirondack region as a 

 whole this much seems to have been shown. There is present a 

 series of completely crystalline limestones and graphitic quartz-schists 

 of sedimentary origin and pre-Cambrian age; closely associated with 

 these are beds of graphitic and other gneisses, which are also sedi- 

 mentary; cutting all the sedimentary rocks are gneisses of igneous 

 origin/certain granites, and the great gabbro mass. That there is 

 present a basal gneiss, while probable, has not been demonstrated. 

 The question is still open. For much the larger part of the region 

 also there remains for future work the discrimination of the sedi- 

 mentary gneisses and the igneous gneisses of later origin. 



The Hthological similarity of the Adirondack sedimentary series 

 with the Grenville series of the Original Laurentian district to the 

 north has frequently been commented upon. In the latter district it 

 has been possible lately to separate the sedimentary gneisses associated 

 with the limestones from the true igneous gneisses of the Basement Com- 

 plex by means of chemical analyses. The success of this method in the 

 Original Laurentian district suggests that it may afford the best means 

 for a satisfactory determination of the origin of the lower gneisses in 

 the Adirondack district. 



Miller 1 describes the occurrence of corundum in gneiss syenite, 

 and quartz-pegmatite of the Laurentian in the counties of Hastings, 

 Renfrew, and Peterborough, in eastern Ontario. 



Adams ■ reports on the geology of a portion of the Laurentian 

 area lying to the north of the island of Montreal. 



A previous report* summarized in this Journal (Vol. VI., pp. 850- 

 8^ covers about the southeastern quarter of this area, and in a 

 general way the conclusions reached for this southeastern area are 

 applied to the larger area under discussion. 



.Economic geology of eastern Ontario, corundum and other -mi neral. by 

 Wu.lett G. Miller Report of the Bureau of Mines, Ontano, Vol. VII., 1898, 

 pp. 207-238. 



- Report on the geology of a portion of the Laurentian area Jying to the north ot 

 the island of Montreal, by Frank D. Adams: Ann. Rep. Geol. Sun. of Canada, 

 Vol. VIII., 1897, part J, pp. 184. With geological map. 



3 Ann Rep. Geol. Surv. of Canada for 1894, Vol. VII., 1896. part J. 



