GEOLOGY OF THE PARADOX LAKE QUADRANGLE 489 



action, and water cementation; that there are all gradations between 

 the three processes, and that under conditions of high temperature 

 and great pressure, water and magma are miscible in all proportions. 

 It would therefore follow that as a center of intrusion was left, the 

 more volatile constituents of the intrusion would be deposited radi- 

 ally and at the same time percolating superheated ground water, 

 containing in solution various constituents from the wall rock, would 

 become mingled with the plutonic material. There would therefore 

 be a gradation between injection processes and cementation. 



These old gneisses seem sometimes to have undergone further 

 cementation with no connection with intrusions. Quartz lenses are 

 frequent in the quartzose gneiss, and so is secondary quartz in micro- 

 scopic quantities. These occurrences belong to the process of 

 cementation of the rock by infiltration of silica in solution. This 

 cementation may have been a continuous process from the time of 

 the first intrusion, but its greatest development must have been sub- 

 sequent to the main intrusion, for the reason that the intrusions were 

 all too deep seated to be in the zone where percolating water could 

 have had much, if any, effect. 



In resume it may be stated that the plutonics were intruded at 

 great depths, some pegmatites being contemporaneously developed 

 at their periphery. The gradual migration to the surface, through 

 the removal by erosion of the overlying burden, gave increasing 

 opportunity for the action of percolating ground water, and the 

 exact line at which the boundary is to be drawn between dike and 

 vein, or between vein and secondary crevice filling or enlargement 

 of original grains, can not be sharply established. 



Dikes. Trap dikes have been noted in several localities. The 

 dikes on Pharaoh lake have already been described in the report 

 previously referred to. They are of diabase, and form an anasto- 

 mosing network running across the strike of the gneiss. These dikes 

 cut pegmatites. They have been more readily weathered than 

 the surrounding gneiss [see pi. 10]. 



There is another diabase dike on the north side of Treadway 

 mountain. It outcrops on the face of a small cliff. 



