THE ARCHEOZOIC ERA. 151 



of the several members of the Archean to one another and to the Proterozoic 

 in certain parts of this region. 



In the Rainy Lake and Lake of the Woods districts of Canada, the Archean 

 consists of (1) Keewatin, 1 metamorphosed basalts, diorites, and other basic igneous 



V^^— .^ r ffi ^ ^ 



Fig. 42. — Figure showing the relations of Archean and Huronian formations in another 

 locality in the Vermilion district of Minnesota. Archean formations : Mqr, Archean 

 granite; JRs, Soudan formation; Me, Ely greenstone. Proterozoic formations: 

 Alo, Ogishkee conglomerate; Alk, Knife Lake slates. Length of section, about 

 5 miles. (Clements, U. S. Geol. Surv.) 



rocks, associated with narrow bands of carbonaceous slate and limestone, 2 

 (2) Laurentian granites and gneisses intrusive into the Keewatin. 



The Archean complex, Keewatin and Laurentian, is also found on the north shore 

 of Lake Huron, where it is overlain by pre-Cambrian rocks, chiefly sedimentary, 3 

 and again in the vicinity of Ottawa, where it is composed mainly of granitoid 

 gneiss (Ottawa gneiss). 4 It is also known at various points about Hudson bay, 5 

 and between it and the Cambrian formation above there are two, and in some 

 places three, great series of clastic rocks separated by unconformities. Through- 

 out all this northern region the relations of the Archean to other formations 

 are usually intricate. 



The Archean in the great southeastern belt has been studied in detail in a 

 few localities. In the vicinity of Washington, 6 D. C, the rocks classed as Archean 

 include gneisses, schists, granite-gneisses, diorites and meta-diorites, gabbros 

 and meta-gabbros, soapstone (altered peridotite and pyroxenite) and granite. 

 Something of their relations is shown in Fig. 43. In an area of western North 

 Carolina 7 where the rocks have been carefully studied, the Archean is divided 

 into five or six formations, made up mostly of gneisses and schists (Fig. 44). 



1 Lawson, Geol. Surv. of Canada, Vol. Ill, Pt. I, F, 1887-8, pp. 99, 100, and 105. 

 Lower Keewatin = Ely greenstone and Soudan formation of the Vermilion region. 



2 Coleman, Bull. Geol. Soc. Am., Vol. IX, p. 224. Coleman considers the Lower 

 Keewatin to correspond to the Lower Huronian ( = Huronian of this Vol.), Rept. 

 Ontario Bureau of Mines, 1900, p. 186. 



3 Logan, Rept. of Progress of the Geol. Surv. of Canada from its commencement 

 to 1863. Bull. 86 and 21st Ann. Rept., U. S. Geol. Surv., Pt. II. Full bibliography 

 given in Bull. 86, up to 1892. The 18,000 feet probably includes some Keewatin. 



4 This is the original Laurentian area. The rocks were formerly known as the 

 Lower Laurentian. Logan, Rept. of Geol. Surv. of Canada, for 1845-46, pp. 40-51. 



5 See reports of Geol. Surv. of Canada. 



6 See references in Bull. 86, U. S. Geol. Surv.; and Keith, Washington (D. C.) 

 folio, U. S. Geol. Surv. 



7 Keith, Cranberry (N. C.-Tenn.) folio. U. S. Geol. Surv. 



