44 



is probably due to the fact that this rock, 

 being softer and more readily eroded than the 

 amphibolite, usually occupies depressions and 

 is thus very frequently largely drift covered. 



303-52 m. St. Ola Station. — Alt. 1068 ft. (325-5 m.) 



488-4 km. At St. Ola the party will again take the train 

 and proceed to Ormsby Junction. 



307-32 m. Ormsby Junction. — Alt. 1,160 ft. (353 -6 m.) 



494-6 km. 



Geology in the Vicinity of Ormsby Junction. 



At this place there are large exposures of the typical 

 "rusty gneiss" (paragneiss) which is so commonly asso- 

 ciated with the crystalline limestones of the Grenville 

 series. In the vicinity of mile post 97 to the west of the 

 station, there are several rock-cuts blasted out to secure 

 the required grade for the railway. This band of gneiss is 

 approximately a mile wide. The gneiss is light grey to 

 very dark grey on a fresh fracture, but weathers with an 

 intensely rusty surface. A typical specimen of the rock, 

 taken from a cutting on the railway track half a mile west 

 of Ormsby Junction, when examined under the microssope, 

 was found to be very fine and uniform in grain and to 

 possess a distinct foliation. It shows a colourless allo- 

 triomorphic base, consisting chiefly of quartz and feldspar, 

 through which are distributed a great number of little 

 flakes of biotite, separate from one another, but all with 

 a marked parallel alignment. The biotite is strongly 

 pleochroic in deep brown and pale yellow colours. The 

 feldspar, which is clear and colourless, shows no twinning. 

 Some of the quartz grains are nearly round and have an 

 appearance strongly suggestive of sand grains. In addi- 

 tion to these minerals there is present as an accessory 

 constituent a small amount of garnet, in individuals 

 having a well-marked polygonal outline, showing that the 

 mineral has a good crystalline form. It is quite isotropic 

 in character. There are also a few little rounded grains of 

 zircon or sphene, as well as a small amount of hydrated 

 oxide of iron, occurring as minute grains, whose form 

 suggests their derivation either from a rhombic pyroxene 

 such as occasionally occurs in rocks of this class, or possibly 

 from pyrite. No pyrite, however, occurs in the sections, 

 neither are there any carbonates present. 



