i9o6.] SMITH— PARAGENESIS OF MINERALS. 207 



gneissic structure, occurs a half mile southeast of the Hopkins reser- 

 voir, three miles southwest of Redwood. In this the feldspar and 

 quartz are still more abundant, and the glaucophane less so. Both 

 rocks appear to be recrystallized diorites, although either may be a 

 metamorphosed dioritic arkose, or an acid adesitic tuff. They would 

 both come under Becker's division of pseudodiorites. 



Ransome^ has described from Angel Island, under the name of 

 "fourchite," a basic dyke rock which is identical with Becker's 

 pseudodiabase. It is only slightly altered, having a little zoisite, 

 and films and needles of glaucophane, the latter developed at the 

 expense of the augite. Ransome found no feldspar in the slides 

 studied by him, but H. W. Turner- found in other slides made from 

 this mass abundant fresh plagioclase, from which he concluded that 

 the so-called fourchite was merely a phase of diabase. The analysis 

 quoted below from Ransome's paper shows that the rock agrees with 

 pseudodiabase and with normal diabases or metabasalts in chemical 

 composition. 



Analysis of "Fourchite" from Angel Island. 



Per Cent. 



Si02 46.98 



AI2O3 17.07 



FeoOa 1.85 



FeO 7,02 



MgO 8.29 



CaO : 12.15 



NaoO 2.54 



K^-0 0.53 



P2O5 0.09 



H2O (loss on ignition) 4.86 



Total 101^8 



III. Diorite. 

 While there are many rocks in the metamorphic series of the 

 Coast Ranges that were probably originally diorites, the writer has 

 observed only one case where the identification was absolutely cer- 

 tain. On Oak Ridge, about five miles east of Calaveras Valley, was 

 found a massive quartz diorite, in which incipient metamorphism 



^ Bull. Dept. Geol. Univ. of California, Vol. I., " Geology of Angel Island," 

 pp. 200-207. 



^ " Notes on Some Igneous, Metamorphic and Sedimentary Rocks in the 

 Coast Ranges of California," Jour. Geol, Vol. VI. (1898), p. 483. 



