Metamorphic and Plutonic Rocks at Omeo. 103 



Mild tliere are also places where the plates of both of the micas 

 are laro-er than the averao^e. Throuo-hout the whole slice 

 there are very numerous small prisms of tourmaline, whicli 

 are translucent in tints of brown, the O ra}'' being brown 

 and the E ray being almost colourless. The prisms are 

 mostly arranged with their C axis in the plane of the slice, 

 and therefore, I observed but few cross sections. So far, 

 however, as I could observe, the prisms are mostly six-sided, 

 and are hemi-hedrally terminated. The size of the prisms 

 varies from -08 inches down to 02 inches in length, and from 

 •04 inches to "01 inches in width. Many of the crystals are 

 much eroded, and also include what appear to be small 

 masses of quartz. 



The second sample examined is of a somewhat fissile o-rey 

 coloured schist, tinted in places with ferruginous stains. The 

 foliations are glistening with minute plates of muscovite, 

 and under the lens one can observe, in addition to them, 

 flakes of brown mica, and numerous prisms of tourmaline of 

 minute size. There are slight traces of nodular structure in 

 this schist. An examination of a thin slice of this rock 

 shows that it is composed of a considerable amount of quartz 

 in grains, intermixed with flakes of muscovite and magnesia 

 mica, the latter being strongly pleochroic. There are great 

 numbers of minute tourmaline crystals distributed through- 

 out the slice. In places the magnesia mica preponderates 

 over the muscovite, as was the case in the sample last 

 described. The principal, if not the only, diflerence in the 

 two samples, is that in the latter quartz is in considerable 

 percentage, and that the magnesia mica occurs in crystals 

 and not in overlapping plates. As I have shown in Fig. 1 , 

 Plate I., portions of the schists have been detached, and are 

 included in the granite. In order to see what changes had 

 been effected b}- the action of the magma upon such 

 fragments of the sedimentary rocks, I examined one such 

 sample (c in Fig. 1, Plate I.) with the following results: — ■ 



The hand sample is a finely crystalline rock, having in 

 places a schistose arrangement ; but taken as a whole, it 

 much resembles some of the very crystalline dark-coloured 

 varieties of hornfels. Under the pocket lens it can be made 

 out to be a mixture of quartz grains, and very numerous 

 minute, splendent, rather short prisms of tourmaline of a 

 black colour. In a thin slice under the microscope, this 

 rock is seen to be composed of quartz grains and very 

 numerous crystals of tourmaline, which is transparent in 



