ARCHEAN GRANITES. 26y 



iBeiitaries, and having no other connection with them. Grant," having first 

 considered the granite as intrusive in the sedimentaries, examined it a 

 second time, and since then has maintained that the sedimentaries are 

 younger than the granite, having been derived from it. 



The sedimentaries lie on the western flank of the granite area extend- 

 ing from Cache Bay of Saganaga Lake on the north to West GruU Lake on 

 the south. Over a considerable portion of this area — for instance, where 

 the drainage is imperfect — exposures are very few, thick morainal deposits 

 covering that part of the area extending approximately from sec. 30, T. GQ , 

 N., R. 5 W., southward into sec. 5, T. 65 N., R. 5 W. At the extreme north 

 and the extreme south, however, Saganaga and West Gull lakes, respec- 

 tively, lie along' the contact and give fairly good opportunities for a 

 study of the existing relations. On the northern exposures especially the 

 relations are so absolutely clear and convincing that the phenomena there 

 observed will be first described. 



Following the international boundary route from west to east, one 

 passes in order through the long, narrow lakes of Knife and Otter Track 

 (Cypress), then through Oak (Swamp) Lalce into a bay of Saganaga Lake. 

 The rocks exposed on these lakes are chiefly slates and graywackes, with 

 occasionally a fine interstratified conglomerate. On Knife Lake the strike 

 of the slates is about N. 70° to 80° E. As we go eastward we note a 

 change in this strike, and when the east end of Otter Track Lake is reached 

 the strike has become N. 45° E. to N. 20° E. and N. 10° E., and even in 

 places is shown as nearly north and south. From Otter Track Lake we 

 cross on the portage a ridge of the slates and then enter Oak Lake (Swamp 

 Lake), where there are exposed over the greater portion of the shores the 

 same dark slates and graywackes that are found on the lakes farther west. 

 On this lake the strike of these sediments has turned until it is west of 

 north. On the east side of the lake the sediments are noticeably different 

 in character from those we have been observing. They are no longer 

 dark, but are light in color — pink to reddish — and instead of being fine 

 slates are predominantly coarse-grained arkoses. They show distinct 

 bedding' and dip, and one can trace gradations from the coarsest-grained 

 rocks into the finer-grained ones. This alternation was noted by earlier 

 observers, but was misinterpreted. These coarse arkoses so closely resemble 



" Grant, U. S., Geol. and Nat. Hist. Survey of Minnesota, Final Eept., Vol. IT, 1899, p. 322. 



