276 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



scope than in the field, for many rocks which were not suspected to be 

 anything but somewhat indurated sandstones are shown by thin sections 

 to be holocrystalHne rocks, here called pseudodiabase and pseudodiorite. 

 Usually, indeed, the transition is somewhat abrupt, and the rule is this: 

 So far as evidence of crushing of the rock masses extends, these are more or 

 less completely crystalline, while, where the rock preserves its continuity, 

 it is generally an ordinary, more or less indurated sediment. The areas of 

 crushed rock are naturally well defined ; for, where the force exceeded the 

 cohesion, the rock broke, but, where the cohesion exceeded the stress, the 

 rock could onl}- be bent or molded. There is no difficulty, however, in 

 finding along the edges of these areas cases of partial conversion to crys- 

 talline material. 



Fig. 7. Partly metamorphosed anticlinal, north fork of Davis Creek. 



The relations of the crystalHne rock to the anticlinal structure on the 

 north branch and to the fissuring of the mass are so indicative tliat it is al- 

 most superfluous to consider the hypothesis of local crystalline precipitates. 

 This theory would not exclude transitions, but it is difficult to imagine that 

 areas of crystalline and uncr3-stalline sedimentation should be so intimately 

 associated with each other. The absence of fossils in the cr3'stalline rocks 

 would also indicate an equally remarkable distribution of areas fitted for 

 animal life. The intense dynamical action evinced wherever the rocks are 

 crvstalline and the absence of similar action in the ordinarj- beds appear 

 to prove conclusively that the crushing and the crj-stallization were asso- 

 ciated phenomena. The microscope finally shows, in connection with the 

 field studies, that the crystallization was a secondary process, the progress 

 of which can be followed in great detail. 



Serpentine. — Tlic grauular and serpentinoid rocks cannot be sharply sep- 

 arated from the unaltered sedimentar}- rocks, as has been pointed out above. 



