94 QUICKSILVEE DEPOSITS OF THE PACIFIC SLOPE. 



this definition in mind the name metamorphic diabase woukl not convey 

 the idea of a metamorphic rock resembhng a diabase, bnt of an ernptive 

 rock changed by metamorphic processes. Even if diabase were usually 

 understood to signify a rock of a certain age and a particular mineral com- 

 position, irrespective of origin, the term metamorphic diabase would be 

 inconvenient on account of its length. If it were in frequent use, it woukl 

 often be contracted to diabase, and this term would lead to misunderstand- 

 ings. It seems eminently desirable to retain for diabase and diorite the 

 meanings which they have long conveyed to geological readers and to limit 

 their application to eruptive masses. Metamorphic rocks which resemble 

 them in mineral composition may then fitly be called j^sendodi abase andjj.se»- 

 dodiorite, and these terms will be employed in the remainder of this report. 



Groups of granular metamorphic rocks. — Tlic gTauular crystalliue rocks of the 

 Coast Ranges ai-e divisible according to their mineralogical composition 

 into several more or less well-defined groups, between whicli, however, 

 there are transitions, as there also are between the granular and the 

 schistose rocks. The chief divisions are pseudodiabase and pseudodiorite. 

 The pseudodiabase is sometimes met in gabbroitic modifications and in 

 a few cases contains so much zoisite that it might without impropriety be 

 denominated a zoisite pseudodiabase; for, since it has been shown that 

 saussurite is either mere zoisite or a mixture of zoisite and plagioclase, 

 there appears to be no reason for retaining that name. The pseudodiorite 

 passes by gradations into a mass so highly hornblendic as to deserve the 

 name of amphibolite. There are also a few rocks in which no augite or 

 amphibole appears, and which are thus composed of feldspar, quartz, zois- 

 ite, etc. These appear to represent pseudodiabase or pseudodiorite in ex- 

 treme forms, since they are locally associated with these rocks, as are also 

 the slightly altered sandstones. 



The schistose rocks are all characterized by tne presence of glauco- 

 phane and zoisite. They are usually micaceous, but sometimes not. 



PSEl'DODIAB.\SE. 



Pseudodiabase is much the commonest of the crvstalline metamorphic 

 rocks of the Coast Ranges. When sufficiently coarse in texture it is readily 



