STRUCTURAL FEATURES OF THE PRE-CAMBRIAN 183 



the rhyolite lava was probably viscous and did not spread out far 

 from its vent. 



Father's Lake area. — The structure of this small area appears to 

 be that of a syncKnal drag fold, although the lack of outcrops on the 

 northwest side of the lake makes its complete determination uncer- 

 tain (Fig. 5). The flows around the southern border of the area 



0/p and Strike 



' Geological 

 Boundary 



Fig. 5. — The Father's Lake area 



are basaltic in composition and quite thin, some of them less than 

 ten feet in thickness. Above them lie one or two flows of por- 

 phyritic basalt, characterized by feldspar phenocrysts up to one-half 



