SECTION OF TEE KEDINGTON. 



289 



studied on former occasions.^ In this case tlie movement has taken phice 

 close to the junction of two rock masses, one metamorphosed, the otlier 

 unaltered, which offered different degrees of resistance. The motion also 

 took place along- a line upon which violent disturbance had occurred at the 

 epoch of metamorphism long before the eruption of basalt. Thus the 

 usual tendency to renewed motion along old lines of movement is once 

 more illustrated. 



no. 10. Uiasianimatic vertical crcss-secti.m of the Redington miue. m, metamoiphlc; », unaUereaNeocomian rocks. 



In the upper part of the mine the disturbance broke the rock into a 

 confused jumble of fragments. It is difficult to imagine how this difference 

 of structure at different levels can have been produced, unless the present . 

 surface is but little beneath the surface as it existed when the fissures were 

 formed. In other words, the lack of s\stem in the fissures of the ui)per 

 mine is an evidence that the fractures are comparatively recent and that 

 the rock near the surface was thrown into confusion because it was not 

 held in place by superincumbent masses. 



Age and genesis.—Thc cvidcuce as to tlie age and tlie mode of genesis of this 

 important deposit consists in a nunlber of facts, each of whicli, if taken 

 singly, may be inconclusive, but all of which are concurrent. It may be 

 well to mention them together. The deposits of the district are grouped 



1 Geology of the Com.stook Lode, Mod. U. S. Geol. Survey No. 3, chap. 4 ; Am. Jour. Sci., 3d series, 

 vol. 30, 1885, pp. 116, 194. 



MON XIII 19 



