222 SMITH— PARAGENESIS OF MINERALS. [Octobers 



into unaltered shales, Junction School-house near Healdsburg ; basic 

 bands of glaucophane schist interbedded with quartz glaucophane 

 schists and gneisses, Tiburon Peninsula ; Angel Island ; Pine Flat ; 

 one mile west of Belmont ; Arroyo Hondo at the northern end of 

 Calaveras Valley. 



11. Certainly Original Igneous Rocks. 



A. Basic Igneous Rocks. — Pseudodiabase ; pseudodiorite ; some 

 greenstones where they grade over into diabasic dykes ; '' four- 

 chites," where they have been partly altered to glaucophane-bearing 

 rocks ; metabasalts of the Roseburg and Coos Bay Folios, Oregon. 

 These rocks all occur as dykes or sills, possible sometimes as old 

 surface flows. In some of the pseudodiorites and pseudodiabases 

 the original minerals and the original structure are so well preserved 

 that no one could doubt their igneous origin. And there is a com- 

 plete gradation from these through rocks where the original struc- 

 ture is preserved, while the original minerals are recrystallized, into 

 schists and greenstones where both original minerals and original 

 structure are lost. This group grades over into basic epidote glauco- 

 phane schists and eclogites. The occasional association of these 

 basic rocks with the acid schists can easily be explained by the 

 hypothesis that the original clay shales and sandstones were in- 

 vaded by dykes and sills of diabase, and that the whole complex, 

 igneous as well as sedimentary rocks, was altered together. 



B. Diorite. — The slightly altered quartz diorite of Oak Ridge 

 five miles east of Calaveras Valley, shows the beginning of altera- 

 tion in the formation of secondary crossite, lawsonite and titanite. 

 The pseudodiorite on San Francisquito Creek, a quarter of a mile 

 below the Searsville dam, Santa Clara County, shows a step further 

 in metamorphism, in that the igneous nature of the rocks is still 

 apparent, while nearly all the minerals in the rock are products 

 of recrystallization. The lawsonite gneiss three miles southwest of 

 Redwood shows the final product from such a rock, where the 

 structure and the minerals are all secondary, and the chemical nature 

 is unaltered. 



A similar beginning of metamorphism has been observed in a 

 syenite from Spanish Peak, Plumas County, where dynamic action 



