CHAPTER III. 



THE ARCHEAN. 



DISTRIBUTION, EXPOSURES, AlfD TOPOGRAPHY. 



The granite described in this chapter belongs to the oldest system in 

 the district, and forms the western elliptical core designated on PL III as 

 Archean. It is surrounded by sedimentary strata, which have a quaqua- 

 versal dip away from the granite as a center. The portion of the Crystal 

 Falls district, in which the granite outcrops, is about 13 miles long by 

 3 miles wide, its longest axis extending in a NW. and SE. direction and 

 covering parts of Ts. 44, 45, and 46 N., Rs. 31 and 32 W. 



The exposures of granite are especially numerous in the southeast part 

 of the oval area, where, owing to the proximity of large streams, the Fence 

 and Deer rivers, and the consequent increased erosion, the drift has to some 

 extent been removed. In the northwest part of the area, with rare excep- 

 tions, all the rocks are deeply covered with drift. 



In general the topography of the area is that of the drift, but in the 

 southern part it is seen to have been consideral^ly influenced by the char- 

 acter of the underlying rocks. The granite usually outcrops in small, 

 rounded, and isolated knobs, whose relations to one another can. only be 

 conjectured. Where an occasional knob is composed of massive granite 

 and more or less gneissoid granite, the exposed surface is so small as 

 to prevent the observer from determining the relations between the two. 

 Cutting the massive and schistose granite are certain long narrow masses 

 of < lark-colored rocks of rather fine grain, and, with few excerptions, very 

 schistose. From their geological occurrence it was concluded, in spite of 

 their appearance, that they are dike rocks cutting the granite. The follow- 

 ing paragraph, quoted from the manuscript notes of C O. Smith, describes 

 very clearly their field occurrence: 



The gaps in this granite ridge seem to indicate greenstone dikes, as here the 

 granite usually has a facing of the greenstone more or less extensive, and often in 

 the center of the gap there are several small areas of greenstone. In all cases the 



