132 OT-iCKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



The epoch of the uphft lies between the end of the period in which the 

 Knoxville and Mariposa beds were deposited and the beginning of that in 

 which the unmetamorphosed "Wallala series was laid down, or, according to 

 the paleontological determinations, between the Neocoraian and a middle 

 Cretaceous period resembling the Gossan. Unless the violent dislocation 

 which took place between these periods was preceded by a gentle uplift of 

 the country above water — and of this no evidence is known — the folding 

 and crusliing which form so prominent a feature of the Coast Ranges must 

 have taken place at tlie close of the Neocomian. 



That tlie metamorphism cannot have preceded the uplift is certain, 

 from the ftict that the confused mass of rubble resulting from dynamic 

 action has often been recemented by the metamorphic processes. The 

 association of the evidences of dynamic action with the alteration is such 

 as to make it clear that the metamorphism was to a great extent dependent 

 on tlie crushing of the rock. There is no evidence that any considerable 

 time elapsed between the crushing and the ensuing chemical changes; but, 

 since the rocks now exposed were then buried at a considerable depth, such 

 an interval might have elapsed without leaving recognizable traces. On 

 the other hand, it appears certain that the metamorphism was effected under 

 different physical conditions from those now prevalent, because, as has been 

 pointed out, the process of decomposition now progressing is inconsistent 

 with the process of recrystallization. It is most natural to suppose the dif- 

 ference to have been one of temperature. Tliat a higher temperature pre- 

 vailed in tlie rocks at the time of the upheaval is also certain ; for tlie 

 crusliing of the rocks was of the utmost intensity and indicates the dissipa- 

 tion, or conversion into heat, of an enormous energy. There is therefore 

 strong reason to suppose that the metamorphism followed immediately upon 

 the upheaval. 



Former depth of the present exposures. — In comparlug tliB uietamorphic Crctaccous 

 rocks of the Coast Ranges with the older crystalline schists, particularly as 

 described by Dr. Lehmann, one point of difference is especially striking. 

 In the older rocks fractures are comparatively lare, and it also appears 

 altogether probable that at a sufficient depth below the surface solids nuist 

 How rather tlinn undergo commiiuition. Hence the intense ])lication of 



