RELATIONS OF THE ARCHEAN. 39 



greenstone is markedly more affected by weathering than is the granite. A study of 

 the relations at the few points of contact did not yield much more than negative 

 results, but these pointed to the intrusive character of the greenstones. 



REI^ATIOlSrS TO OVBELYKSTG FORMATIOlSrs. 



The relations of the granite to the sedimentary rocks might be explained 

 in two ways; the former may serve as the base of the latter rocks, or it may 

 penetrate them. The occm-rence of the granite in an elliptical shape, with 

 sediments sm-rounding it showing quaquaversal dips, might be regarded as 

 evidence of its intrusion in the Hm-onian sediments, and on this theory it 

 would follow that the granite is of Huronian or post-Huronian age. If 

 intrusive, it should be found to penetrate and metamorphose those sedi- 

 ments. Against the intrusive character of the granite, and in favor of its 

 pre-Huronian age, are the following facts: (1) There is a total absence in 

 the surrotmding sedimentary strata of any dikes which are related to the 

 granite. (2) There is a total absence of any metamorphic action, so far as 

 observed, in the sedimentaries. (3) On the east flank of the granite core, 

 on the west bank, of the west branch of the Fence River in the SW. corner 

 sec. 1, T. 45 N., R. 32 W., is a recomposed granite, which passes up into a 

 fine sericitic quartzite, with false bedding. These rocks evidently derived 

 their material from the granite, and hence mark the beginning of sedimenta- 

 tion in this area. 



Thus the positive evidence confirms the negative, and since the granite 

 underlies the oldest sedimentary rocks, whose pge has been determined to 

 be Huronian, the former is classified as Archean, that term being used here 

 to designate those rocks of undoubted igneous character which form the 

 foundation upon which rest the oldest determinable sedimentary rocks. 

 It is not the province of this paper to enter into a speculative discussion of 

 the origin of the Archean rocks of the district. For such a discussion the 

 reader is referred to Professor Van Rise's exhaustive disquisition on the 

 Principles of North American pre-Cambrian Geology,^ where the conclusion 

 is reached that "the Archean is igneous and represents a part of the original 

 crust of the earth, or its downward crystallization."^ The Archean has 

 gradually reached the surface by the removal by erosion of the superjacent 

 rocks. 



' Sixteentli Ann. Rept. U. S. Geol. Survey, Part I, 1896, pp. 571-874. 

 'Loc. cit., p. 752. 



