OROGRAPHIC MOVEMENT AND METAMORPIilSM. 01 



These conditions are undoubtedly due in large part to the lack of a 

 fused upwelling magma along the line of weakness. Lateral comi)res- 

 sion must have been the chief cause of this pre-Cretaceous upheaval. 



CORRELA TION OF THE UPHEA VAL. 



The recent work of the United States Geological Survey has demon- 

 strated the Mesozoic age of the greater part of the granite of the Sierra 

 Nevada. It seems to be the opinion of a number of paleontologists, 

 among whom are Professor Hyatt and J. P. Smith, that the youngest of 

 the sedimentary rocks involved in this U])heaval belong to the Jurassic 

 rather than to the Cretaceous, a fact for which the writer has contended 

 on stratigraphic and lithologic grounds. This revolution in the Sierra 

 region can be traced into the Klamath mountains, where the granite of 

 the Trinity mountains is intrusive in slates, a ])art of which Mr Diller 

 considers as belonging to the Jura-Trias. The effects of this stupendous 

 revolution in the region of the Sierra Nevada and of the Klamath moun- 

 tains, accompanied by the upwelling of a great granitic magma, must 

 have been felt to a considerable distance. At the same time the pre- 

 Cretaceous series of the Coast ranges experienced its first elevation 

 from beneath the ocean. Toward the south the axes of uplift corre- 

 sponded in part to the ancient granite ridges against which this series 

 was dei)0sited and in part were independent of them. Between the 

 Trinity mountains and San Francisco bay the elevation and enormous 

 erosion which has taken place since has brought to light no central axis. 

 A series of ranges was formed with a trend slightly more to the west than 

 the course of the elevation as a whole. All evidence at hand 2>oints to 

 the fact of the first upheaval of the pre-Cretaceous series of the central 

 and southern Coast ranges as being coeval with that of the Yallo Bally, 

 Trinity and })lexus of mountains to the northwest, which closed the 

 Jurassic. In the Coast ranges proper there was no breaking and tilting 

 back of the sedimentary series by a fused granite core. The movement 

 was marked by a folding and crushing together of the strata to form a 

 series of more or less parallel elevations. 



METAMORPIilSM INCIDENT TO THE MOVEMENT. 



Dynamic Metamorphism. — During the period of elevation and deforma- 

 tion the dynamic metamorphism took place, being more intense toward 

 the north. Through the C'oast ranges south of the Klamath mountains 

 this metamorphism was not great, though the rocks are referred to in 

 geologic literature as " metamorphic." With local exceptions, they are 

 uncrystalline, and only rarely have secondary minerals been formed. 



Chemical Metamorphisni. — Probaljly following the upheaval, and during 



