126 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



It has doubtless happened in times past that observers have attempted to 

 cut the gordian knot of metaniorphism by assuming such repLicements as 

 seemed convenient. This method of deahng with the subject is as super- 

 ficial as a flat denial of all conceivable methods of genesis, excepting one, of 

 a certain product. 



General course of serpentinization. — Having statcd iu detail tlic cliavacter of the 

 evidence as to the serpentinization of the mineral constituents of the sand- 

 stones and the granular metamorphic rocks, it only remains to indicate the 

 course of the transformation as a whole. In the sandstones which have 

 merely weathered, but which have not been subjected to even incipient 

 recrystallization, or, in other words, in the sandstones of later age than the 

 Neocomian, serpentine has not been detected with certainty, though it has 

 been carefully sought, while chlorite is common. I know of no reason, 

 however, why small quantities of serpentine should not hereafter be found 

 in these rocks. There is abundant evidence that serpentinization was not 

 widespread or important in the later rocks, but this does not exclude local 

 or partial repetition at later dates of the conditions which induced serpen- 

 tinization at the close of the Neocomian. 



One of the important results of this investigation is that the slightly 

 recrystaUized, older sandstones were subject to serpentinization as well 

 as those which had undergone complete transformation. In these rocks, 

 of course the more permeable aggregates yielded most I'eadily to attack 

 and were first aff"ected by the change. In such cases the phenomena of 

 recrystallization and serpentinization may be studied side by side, and it 

 is rarely the case that some small patches and streaks of serpentine are 

 not observable in these sandstones. At a further stage the interstitial space 

 between the remains of the clastic grains is almost wholly filled with ser- 

 pentine, which then attacks these nuclei, as has been described, though, as 

 might be expected, the process is irregular, so that one portion of a slide 

 is often more serpentinized than others. The quartz appears to yield more 

 slowly to serpentinization than the feldspar, and this more slowly than the 

 fine-grained cement. The extent of surface exposed is of course an im- 

 portant factor. As the amount of the serpentine increases, traces of grate- 

 structure make their appearance; but, though this fact is easily established. 



