(CONDITIONS OF ^METAMOKPfllSM. 133 



sucli rocks, ill wliich even crystals of feldspar are bent at sharp angles 

 instead of breaking, indicates tliat they have been subjected to mechanical 

 forces of great intensity while under immense pressure or when buried at 

 a great depth. In the Coast Ranges, on the other hand, the metamorphic 

 rocks have been crushed to an astonishing degree. This is especially 

 observable in the phthanites, which are often intersected by so fine a net- 

 work of minute fissures, now filled with quartz veins, that a portion of the 

 net is visible only under the microscope. Plication of strata is indeed 

 e.\tremely frequent ; but, at least in a great proportion of cases, this has 

 not been accomplished to any great extent by Hexure of the rock mass. It 

 was attended by the formation of innumerable cracks, which have gaped 

 more or less and thus permitted readjustment without great displacement of 

 the fragments. The fragments having been receraented in their new posi- 

 tion, the strata became once more coherent. Often also the rocks have 

 been crushed to a mere, confused mass of rubble, in which the original 

 stratigrapliical relations are entirely obscured. These relations appear to 

 demonstrate not only the expenditure of enormous energy, but also that 

 the Cretaceous rocks at the time they were metamorphosed were not buried 

 at great depths, perhaps not more than two or three thousand feet below 

 the surface. This being granted, it may readily be understood that, even 

 if the character of the rocks and of the metamorphism in the Archaean 

 were exactly similar to that of the Cretaceous strata of the Coast Ranges, 

 the latter would inevitably be less uniformly altered, while at least the 

 quantitative relations of the products of alteration in these mountains 

 would probably differ from those characteristic of similar masses altered 

 under a far greater and far more uniform pressure. 



Dynamic conditicns. — The Post-Neocomiau uplift was accompanied by in- 

 tense compression in a northeast and southwest direction. The strata of 

 the Coast Ranges were partly plicated and partly crushed, while on the 

 gold belt they were driven into a nearly vertical position. Both areas 

 appear to have been and still to be underlain by granite at no very great 

 depth. What the bed rock in the great valley of California may be is 

 not definitely known, but there seems no reason to suppose that it is not 

 granite there also. It is impossible to suppose any force which would 



