Geology 



closely related to granite, but having been cooled more 

 rapidly than that rock, is somewhat finer in grain and 

 frequently contains some glass by way of ground-mass, 

 in which crystals of quartz, felspar, and a little mica are 

 embedded. 



The crystals of felspar in these dykes were, in some 

 instances, upwards of an inch in length and were very 

 perfectly formed, showing that they must have been 

 produced under conditions of slow cooling, probably in a 

 great granite reservoir, while the fine-grained ground- 

 mass indicated much more rapid cooling, such as may 

 have been caused by the injection of the molten matter, 

 with its floating crystals, into the crack or fissure where 

 it eventually solidified to form the dyke. 



In a small tributary which entered Centre Valley 

 from the north we found in some gravels several crystals 

 of tourmaline and some small pebbles of tin-stone, together 

 with numerous rounded masses of granite similar to that 

 previously encountered here and there in the lower part 

 of Centre Valley. We made a note to explore Tin 

 Creek, as we named this stream, on our return journey, 

 should time permit. 



We now reached the foot of a moraine much higher 

 and more massive than any which we had as yet en- 

 countered, and on reaching its summit found a large 

 lake occupying nearly the whole width of the valley on 

 its upper side. The outlet of the lake was not in the 

 centre of the valley but on its western side, and on 

 visiting it we found that the stream occupied a deep 

 gorge in the solid gneiss. 



When the ice had retreated from the moraine the 

 lowest part of this had evidently been at the western 



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