236 



QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



blocks are very frequently so displaced that there is an utter discordance 

 between the various dips observable in a single cropping of a few feet in 

 diameter. That there may be predominant faults (Daubree's paraclases), as 

 well as the innumerable piesoelastic fissures, is not improbable ; but between 

 the extreme disturbance shown by the exposed rock and the proportion of 

 the surface covered by soil this could not be determined. ( )nly one result 

 Avas obtained b}' the study of dips. I'his is, tliat the ridges are mainly 

 s3-nclinal folds, so that the prevalent di[) of the Knoxville beds is into the 

 hills. Tliis result is not unimportant, because it .shows that the region is 

 deeply eroded and establishes another point of resemblance between the 

 rocks of tliis group here and elsewhere. 



The degree of metamorphism of the Knoxville beds of Clear Lake 

 varies greatly. Some of the sandstones are extremely little altered and 

 are characteristic micaceous arcose. ( Jranular metamorphics, glaucophane 

 schists, and serpentine also occur; but the transitions are so frequent and 

 seemingly so capricious that it would be impossible to define the different 

 varieties by areas. 



Fio. 5. Ruptures i>ro(hiceil by corapieaaion ufstiata. 



structu e of the ranges. — T'hc regularity of soHic of the ranges is in strong 

 contrast to the irregular disposition of the strata and is possibly duo to tlie 

 combined effect of plication and metamorphism. If a series of beds is 

 thrown into folds, as in the accompanying diagram (Fig. 5), it is clear 

 that the upper surface of the anticlinals will tend to crack open and also 

 that a similar tendency will exist in the lower surface of the synclinals. 

 If metamorphism is then induced by rising waters holding mineral matter 

 in solution, such as silicic acid, the compressed under surface of the anti- 

 clinal will offer a resistance to percolation, while the fractured under sur- 



