G. F. Becker — Metamorphie rocks of California. 357 



latter. The granite as well as the strata above it must there- 

 fore have been disturbed and laterally compressed at the close 

 of the Neocomian. Many thousand square miles of exposures 

 of rock shattered until the average size of the unbroken lumps 

 does not exceed that of an egg indicate the amount of energy 

 converted into heat in this process. Before the upheaval, the 

 sandstones and even the granite must have contained water 

 which was warmed by this heat and, since the action was com- 

 pressive, interstitial space must have been reduced, tending to 

 force the solutions formed to the surface along the lines of 

 fracture. Under these conditions chemical transformations 

 were inevitable and it is as nearly as possible certain that these 

 would not be confined to a mere molecular rearrangement of 

 the constituents of the sedimentary rocks, but that the granite 

 also would be involved. 



Without entering into any discussion of the chemical pro- 

 cesses here, it is sufficient to state that the indications of field 

 study are that the solutions were at first very warm and basic 

 and that the earliest stage of the process of metamorphism was 

 the conversion of the sandstones and some shales to non- 

 crystalline rocks carrying augite and amphibole. Serpentiniza- 

 tion seems to have followed at a lower temperature and finally 

 ensued silicification, the solutions having now become acid. It 

 is possible, and even probable, that silicification went on in 

 part contemporaneously with the other processes, but under 

 different physical conditions. The evidence, however, is on the 

 whole against the supposition that the silicified rocks now ex- 

 posed were thus modified contemporaneously with the forma- 

 tion of the basic metamorphie rocks of the present surface. 

 Chloritization and impregnation with calcite and gypsum are 

 still going on at ordinary temperature. 



In conclusion it may be noted that all the more important 

 minerals of the Archean schists are found in the metamorphosed 

 rocks of the Coast Range?. The quantitative relations indeed 

 are different, especially those of the feldspars ; for while ortho- 

 clase predominates in the Archean, plagioclase is much more 

 common in the Coast Ranges. These^ is far less evidence 

 of great pressure in the quicksilver belt than in most Archean 

 areas, and the intensity of chemical action has been much less 

 uniform ; but it is evident that under conditions not greatly 

 dissimilar to those which prevailed in California at the close of 

 the Neocomian, rocks not distinguishable from those of Archean 

 areas might have been formed. Indeed more than one eminent 

 geologist has believed that he recognized the rocks in question 

 as Archean. It does not follow, however, to my mind, that all 

 Archean rocks are necessarily of an origin similar to that of 

 the metamorphosed rocks of the Coast Ranges. 



San Francisco, Office TJ. S. Geol. Survey, Feb., 1886. 



