rSEUDODIABASE. 99 



rite appears due to the decomposition of tlie augite. Zoisite is not verv 

 abundant in this sUde, but is present iu cliaracteristlc prisms. Ihnenito 

 and leucoxene are frequent. 



Xo. r>n. Sulphur Bank, is a dark-green, fine-grained, crystalline rock, 

 iu which feldspars and bisillcates can be seen with the naked eye. Under 

 the microscope all tlie feldspars appear to be twinned and those which 

 are favorably placed for examination give angles of extinction appropriate 

 to oligoclase. The slide contains a little quartz. The pyroxene is mostly 

 in the form of small grains, but there are some larger crystals givino- the 

 angle of extinction of augite. The mineral is almost colorless. The slide 

 also contains one hornblende prism. Titanic iron and unquestionable tran- 

 sitions from this to titanite are common. 



This slide shows notable secondary changes. Uralitization, whicli is 

 so conniion in the pseudodiabases, is here entirely absent. The augite de- 

 composes directly into serpentine and chlorite, both of which are abundant. 



A complete analysis of this rock was made. The composition is ex- 

 tremely similar to that of No. 21, Coast Ranges, given above: 



Loss at 100'-, H-0 0. :fc;) 



Loss above 100°, H-0 o %5 



Silica, SiO« .->1.278 



rhosphoric acid, P'0= 0. 131 



Titanic acid, TiO- 1.330 



Alumina, AI-0^ l.^,_ q4,^ 



Ferric oxide, Fe-C 2.415 



Ferrous oxide, FeO 8.014 



Nickel oxide, NiO 0.098 



Manganous oxide, MnO 0. 251 



Lime, CaO 7. 07i) 



Magnesia, MgO ,;. 009 



Soda, Ka-O 4.433 



Pot assa, K-0 q j.^^ 



Total 09.(i23 



The atomic ratio deduced from this is H" : R" : R" : Siz=0.o73 : 0.931 

 : 0.*t74 : 3.419. 



rSKUDODIOKITE. * 



The pseudodiabase passes by transition into galjbroitic modifications 

 on the one hand and into i)seudodiorite on the other. There is no o-ener;il 



