264 AUSTRALASIAN ANTARCTIC EXPEDITION. 



This is particularly true in the case of Nos. I and V. In the latter as compared 

 with the former there is an increase in normative quartz and magnetite, which is offset 

 by a decrease in hypersthene. This is due to the oxidation of the FeO into Fe 2 3 , 

 which causes more of the FeO to be required for normative magnetite, decreasing the 

 amount available for diopside and hypersthene, and consequently liberating SiO a for 

 normative quartz. 



It is interesting to note, in passing, the possible effect of slight weathering on 

 the norm, and perhaps too on the magmatic designation of a rock. It is quite conceivable 

 that by the oxidation of the FeO, and the consequent liberation of normative Si0 2 , a rock 

 which actually contains modal olivine may show normative quartz. Further, the 

 diversion of this Si0 2 from the femic to the salic portion of the norm would disturb th e 

 relative proportions of salic and femic constituents and of normative quartz and felspar' 

 putting the rock into a more salic class and a more quaric order. 



In the present instance the disturbance has not been sufficient to change the 

 magmatic position of V relatively to I, and both rocks belong to III. 5. 4. 3 Auvergnose. 

 No. Ill, is placed in IH.4.4.3. 



CONCLUSION. 



The wonderful similarity between the quartz-dolerites of South Victoria Land 

 and those of Tasmania has been pointed out by Benson 1 and Thomson 2 . The present 

 writer has had the opportunity of examining some of the Tasmanian rocks microscopical^ 

 and of comparing them with the Adelie Land rocks, and the resemblance is certainly 

 remarkable. Chemical and mineralogical investigation indeed show that the rocks 

 at present under discussion are very closely related to those of Tasmania, and that they 

 are, beyond reasonable doubt, co-magmatic with the dolerites of South Victoria Land 

 encountered by the Scott and Shackleton Expeditions. 



II. DOLERITE ERRATICS FROM THE MORAINES, CAPE DENISON. 



The collections made from the moraines near the Winter Quarters at Common- 

 wealth Bay have yielded a number of specimens that have features in common with 

 the dolerites described above, and should be grouped with them. 



Specimen No. 837, of which No. 838 is a duplicate, appears in hand-specimen 

 as a dark, fairly compact rock, somewhat pitted on the weathered surface, and showing 

 occasional small phenocrysts of felspar. Under the microscope the rock is seen to be 

 a typical fine-grained dolerite, wherein the pyroxene is predominant over the felspar, 

 and resembling No. 732B in many respects. The felspar is present in two generations, 



1 Op. cit, ' Jour. & Proc. Eoy. Soc. N.S.W., vol. xliii, 1911, p. 312. 



