208 SMITH— PARAGENESIS OF MINERALS. [Octobers, 



was observed. The original minerals were oligoclase, quartz, and a 

 brown titaniferous hornblende, probably kataphorite. This rock 

 has been slightly crushed, and the feldspars partly decomposed, set- 

 ting free part of the albite and anorthite molecules. The albite did 

 not crystallize out as such, but joined itself to the amphibole mole- 

 cule, forming a glaucophane-like mineral, crossite, around- the border 

 of the undecomposed kataphorite. The crossite contains no titanium, 

 and that constituent has taken up some of the lime to form titanite, 

 and in other places has formed leucoxene. The anorthite molecule 

 simply took up water and formed lawsonite, which occurs in and 

 around the oligoclase in slender prisms. This rock is not a schist, 

 nor even a gneiss, having probably been metamorphosed under mass- 

 static conditions. Glaucophane schists were seen near the diorite, 

 but they were apparently of more basic material. The agencies that 

 made the schists also affected the diorite, but to a less extent. 



On Spanish Peak, in Plumas County, at the northern end of the 

 Sierra Nevada, the rocks have been much affected by dynamic ac- 

 tion, quartzites having been changed to sericite schists, and con- 

 glomerates having been granulated until they have become fine- 

 grained micaceous quartzites. At this place was observed a massive 

 syenite that shows in thin sections the results of dynamic meta- 

 morphism. The rock was originally an albite, plagioclase hornblende 

 mass, and most of the original minerals are intact. But the feldspars 

 have become clouded through incipient decomposition, and the 

 original brown hornblende has frayed out on the borders to a felt 

 of asbestiform blue amphiboles that have the physical properties of 

 crocidolite. Their pleochroism is intense, but lacks the violet shade 

 that glaucophane and crossite always show. Their genesis is cer- 

 tainly the same as that of the crossite in the quartz diorite of Oak 

 Ridge, from the addition of the albite molecule to the hornblende. 

 This mineral was titaniferous, and the secondary crocidolite could 

 not retain the titanium, which has then, as in the Oak Ridge diorite, 

 separated out as titanite. This rock has not become a glaucophane 

 schist, and none are known in the Sierra Nevada. Neither lawsonite 

 nor epidote has been formed in the syenite, for the original feldspar 

 was probably too acid to furnish the lime necessary for the formation 

 of these minerals. 



