ARCHEAN GRANITES. 273 



of this rock can uot be definitely recognized in all cases, bnt since it is 

 analogous in all respects to the material described above as occurring 

 between the granite and the clearly recognizable sediments, it is assumed 

 to be the schistose arkose that lies between the granite and the overlying 

 sediments. These sediments consist of interbedded slates, gray wackes, and 

 conglomerates, and in these conglomerates pebbles were observed which 

 could be identified with the granite of Saganaga Lake. After a study of 

 the exposures here there can be no reasonable doubt that the sediments are 

 younger than, and partially derived from, the adjacent granite of Saganaga 

 Lake. 



Within the area shown on the map forming fig. 17 there is a knob of 

 greenstone, penetrated by numerous dikes of granite, similar to those 

 occurring in the greenstone adjacent to the granite of Saganaga Lake at 

 other places in this district. These dikes are presumed to be offshoots from 

 the granite. Overlj'ing this granite are sediments similar to those overlying 

 the not far distant granites, consisting to a considerable extent of pebbles 

 of granite and greenstone, showing them to be younger than both the 

 greenstones and the granite. Within this small area, therefore, we find 

 the Archean greenstone, the granite of Saganaga Lake, and the Lower 

 Huronian sediments, with their relations to one another clearly shown. 

 The Lower Huronian sediments are now folded into synclines within the 

 granite and greenstone, and hence wrap around these rocks, as is shown 

 on the accompanying map (fig. 17). 



METAMORPHIC EFFECTS OF THE GRANITE OF SAGANAGA LAKE. 



The granite of Saganaga Lake having been found intrusive only in the 

 greenstones of Archean age, we are able to study its metamorphic effects 

 upon these rocks alone. These eff"ects are in all respects the same as those 

 produced upon the similar greenstones by the intrusion of the granites of 

 Trout, Basswood, and Burntside lakes, as the result of which amphibolitic 

 schists were produced. The processes of metamorphism induced by these 

 intrusions and the products resulting therefrom have been described in 

 preceding portions of this monograph (p. 156 et seq.). 



INTERESTING LOCALITIES. 



Exposures of the granite of Saganaga Lake are so extensive in the 

 area in which it occurs that it is unnecessary to refer to anj^ special locality 

 at which its characters may be studied. There are, however, several places 



MON XLV — 03 18 



