DIORITE INTEUSIVES. 



231 



Similar gradations have been noted by Becke in the tonahte from the 

 Rieserferner.^ The diorite massif of the Crystal Falls district seems to cor- 

 respond very closely to the granodiorite masses of Becke, Turner, and Lind- 

 gren,^ which on the one hand grade into the granitites and on the other into 

 the diorites. 



ANALYSIS OF DIORITE. 



It has not been found possible thus far to obtain analyses of all these 

 varieties. The more acid facies of the diorites seem in their mineralogical 

 composition to show very clearly their gradations toward the tonalites and 

 granites. This being the case, it was deemed of more importance to study 

 the relations of the more basic dioritic facies in order to detemiine the rela- 

 tionship of these rocks to those of the more basic gabbro and peridotite 

 families which are found in association with them. To this end an analysis 

 of one of the mica-diorites was obtained. 



This rock contains the dark constituents, biotite and hornblende, in 

 large quantity, and of these the mica predominates. Plagioclase predomi- 

 nates among the white silicates, with orthoclase and quartz very subordinate. 

 The mica is considerably altered, but on the whole the rock is fairly fresh. 

 Fig. -B, PI. XXXIX, is a photomicrograph of the rock and shows its general 

 characters. The following analysis was made by Dr. H. N. Stokes, in the 

 laboratory of the United States Geological Survey: 



Analysis of diorite. 



'Petrographische studien am Tonalit der Eieserferuer, by F. Becke: Tscherraaks mineral. Mitt- 

 heil., Vol. XIII, 1892, pp. 379-464. 



-The granodiorite of California ajjpears from Lindgren's description (Granitic rock.s of Cali- 

 fornia, by W. Lindgren : Am. Jour. Sci., 4tb series, Vol. Ill, 1897, p. 308; where can be found references 

 to mention and descriptions of granodiorite) to correspond very closely to toualite, though Turner 

 uses the name as synonymous with quartz-mica-diorite (Geology of the Sierra Nevada, by H.W. Turner: 

 Seventeenth Aun. Kept. U. S. Geol. Survey, Part I, 1896, pp. 636,724). 



