THE HEART OF THE ANTARCTIC 



partly explains the survival of lichens high up on the 

 slopes of Erebus. It also has the effect of prolonging 

 a superficial local thaw from summer far into spring, on 

 the one hand, and autumn on the other. Such, a great 

 diurnal range of temperature, combined with the effects 

 of summer thaw followed by the severe frosts of winter,- 

 exerts a powerful disrupting force upon the rocks, and 

 accounts for the extensive rubble banks and sheets and 

 patches of loose and broken felspar crystals, which are 

 spread over such a large area of country near Mount 

 Erebus, &c. At our winter quarters at Cape Royds we at 

 first mistook these for beds of volcanic tuff. 



Volcanic Rocks 



Ross Island.— As the chief varieties of volcanic rocks 

 met with in Ross Island have already been described by 

 Messrs. Ferrar and Prior, a brief description of these will 

 suffice. 



At Ross Island we particularly studied the relations 

 to one another of the three principal types of rock there 

 developed, viz., kenyte, trachyte and basalt. We are now 

 in a position to say that, on the whole, the trachytes appear 

 to have been the oldest rocks, the kenytes to be of inter- 

 mediate age, and the basalts the newest. The evidence for 

 this is as follows: 



On the western slopes of Mount Erebus, above our 

 winter quarters, specimens were not infrequently found 

 of what at first sight appeared to be fragments of sand- 

 stone enclosed in kenyte lava. A closer inspection of these 

 showed that they were in reality varieties of trachyte. 

 Similar specimens were met with in the kenytes near Cape 

 Barne. It would seem from this that the oldest lavas in 

 this area were trachytes, and that later kenyte eruptions 

 followed, which partly destroyed the trachytes, and thus 



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