224 W. LINDGREN — CALIFORNIA GOLD-QUARTZ VEINS. 



acted on by the dynamo-nietamorphic processes which also affected the 

 sedimentary rocks, and are largely converted into crystalline schists. It 

 may be said in general that the sedimentary rocks prevail in the eastern 

 part of the metamorphic belt, while along the great valley basic, igneous 

 rocks are found in the greatest abundance. The granitic rocks of the 

 high Sierra Nevada are to a large extent granodiorites, the name adopted 

 on the survey maps for a quartz-mica-diorite containing more or less 

 orthoclase. In the metamorphic series there are many smaller masses 

 of the same rock — the latest intrusions — which are usually but little 

 affected by dynamo-metamorphic processes. 



The intimate connection of the gold deposits with the metamorphic 

 series or the auriferous slates has been recognized for a long time, and 

 Professor Whitney emphasizes it repeatedly in his works. The auriferous 

 region, indeed, corresponds closely with the extent of the metamorphic 

 series. Even in the south, where the granitic rocks predominate, it has 

 been shown that the gold deposits are usually connected with the scattered 

 schist areas. Few gold-quartz veins are found in the granitic area, and 

 then usually near the contact. Within the typical gold-bearing region 

 the veins are distributed with remarkable impartiality, and occur in 

 almost any of the great variety of rocks which make up the metamorphic 

 series. They are found in granite, diorite, granodiorite, gabbro and ser- 

 pentine ; in quartz-porphyrite, augite or hornblende-porphyrite and dia- 

 base ; in amphibolite and other dynamo-metamorphosed rocks ; in sedi- 

 mentary, more or less altered slates, sandstones and limestones. In 

 Tertiary volcanic rocks gold deposits are only found on the eastern slope 

 of the range. It is apparently impossible to formulate any law as to 

 their lithologic occurrence or to say that they prevail in any one kind of 

 rock in the metamorphic series. 



Regarding the quartz-veins of California F. von Richthofen has made 

 a frequently quoted statement which in a certain sense may be correct, 

 but which unless qualified is apt to lead to grave errors. It is as follows : * 



The auriferous quartz veins "have in their occurrence clearly discernible con- 

 nection with the extension of the granite. They are crowded closely at its contact 

 with the metamorphic rocks, and occur here partly in the former, partly in the 

 latter. The greater the distance from the granite, the rarer they become in the 

 metamorphic rocks, and only occur as an exception where the influence of the out- 

 cropping granite would not be expected on account of its distance. In the same 

 way they become less frequent in the granitic regions as the distance from the con- 

 tact increases, and are, as a rule, entirely lacking in the interior of the large granite 

 masses." 



This statement cannot be accepted for the main granitic contact, which, 

 on the contrary, except near Sonora, is remarkably barren of important 



*Zeitschrilt der deutschen Geol. Gesell., B. xxi, 1869, p. 727. 



