GLAUCOrUANE SCUIST. 103 



pliiine are also macroscopically visible. Under the microscope a great 

 portion of the rock is seen to l)e made up of interlocking grains of quartz 

 and unstriated feldspar. In tlie Thoulet solution a oonsiderabhi amount of 

 feldspatliio material floats at ;15!), and this gives a strong potash reaction, 

 sliowing that the material Is at least in part orthoclase. Higher specific 

 gravities and cheuiical tests sliowtliat plagloclase is also present. The slide 

 contains a mimber of large glaucophane crystals, son^e of them, which are 

 cut across tlie principal axis, exhibiting tlie characteristic amphibolo prism 

 and cleavage. The optical properties are as described on a pre\-ious page. 

 There are few mlcrolltes of glaucophane. 



l']mbedded in the mass of feldspar and quartz are numerous green 

 hexao'imal foils, whicli give the optical reactions of mica and are solulde witli 

 difficulty in hot sulphuric acid. The mineral is probably a biotlte. White 

 mica is also present. The scales of this mineral cannot well be separated, 

 but in a similar rock (No. 117, Coast flanges) white mica is present in foils of 

 considerable size, wlilcli can be separated. Tliey show a large angle between 

 the optical axes, and are therefore probably muscovlte. Zolsite is abun- 

 dant in Xo. 31, in well developed, pointed prisms with terminal faces. It is 

 greenish and slightly dlchroitic, which is unusual. Tlie slide contains a few 

 garnets and nmch titanlte. Some well developed rhombs of the latter nnn- 

 eral include ihnenite grains. Apatites, zircons, and a little chlorite con- 

 nected with the biotlte were observed. In the groundmass are groups of 

 long, colorless, radiating fibers, which appear to extinguish light in the 

 direction of the main axis and when densely massed give very vivid inter- 

 ference colors. These properties correspond to fibrolite, and, did these 

 needles occur in a true gneiss. Instead of in a Cretaceous, metamorphic rock, 

 no hesitation would be felt In Identifying tluMii as such. Under the cir- 

 cumstances and in the absence of opportunity for determining their specific 

 gravitv, it is not safe to pronounce on their composition. 



Xo. 147 corresponds in some particulars to the rock just described ; 

 brilliant, brown l)iotIte, however, with characteristic interference figure, 

 replaces the muscovlte, and a small portion of the feldspar shows striations. 

 The glaucophane is in all respects similar. Apatite is present, but zoisite 

 could IK it ])G identified wltli ccrtaintv. 



