DESCRIPTION OF THE AREAS 279 



Quartz-porphyrjr occurs as dikes cutting the greenstone and seems 

 likely to be a minor intrusive phase of the period of volcanic activity. 



The Granite 



The surface consolidated rock of the greater part of the area is a fresh 

 massive granite that weathers to a faint pink. It has been found intrud- 

 ing both the lower and the upper members of the pre-granite complex, 

 but has not been found cutting the quartz porphyry. The fresh and 

 unaltered character of the granite is fairly conclusive evidence that it is 

 younger than the sheared and altered quartz porphyry. 



Relations of the Sedimentary and Volcanic Groups 



Groups of the pre-Granite Complex 



It is believed that the dominantly volcanic group of rocks is younger 

 than the dominantly sedimentary group, but that the two are not sepa- 

 rated by any unconformity and are a thick, practically continuous series. 

 This conclusion is based on the following facts : 



1. The rocks of the sedimentary group in proximity to the volcanic 

 group have dips that vary from 90 to 60 degrees. Where the beds are not 

 vertical the dip is in all cases underneath the greenstone series. 



2. The rocks are not overturned, since at one exposure at least the evi- 

 dence seems conclusive that the top of beds dipping underneath the green- 

 stone is toward the volcanic rock. 



3. At one locality there seems to be a gradation from one group to the 

 other. 



The top and bottom of the section is determinable in an exposure on 

 the south shore of the lake one and one-half miles west of the trail to 

 Gods Lake. The dip of the beds at that point is 60 degrees north. At 

 the southern part of the section are well banded slates alternating with 

 hard quartzitic layers. Northward there is a flow of andesite 10 feet 

 thick, succeeded by a thick band of fragmental material, conglomeratic 

 or possibly in part tulfaceous. To the north of this is a flow of basic rock 

 of basaltic character which becomes finer in texture toward the north. 

 A few hundred feet northward, across an arm of the lake, is the typical 

 ellipsoidal weathering greenstone of the upper group of the complex. 

 (See figure 2.) 



At the contact of the fragmental rock with the andesite flow there 'are 

 distinct tonguelike projections of the fragmental rock into the andesite. 

 (See figure 3.) This seems to be most satisfactorily explained on the 

 assumption that the surface of the lava flow cracked during cooling and 



