PETROLOGY OF ROCK COLLECTIONS 



FROM THE MAINLAND OF SOUTH VICTORIA LAND 



BY 



D. MAWSON, D.Sc, B.E. 



University of Adelaide 



The material described is included in three collections made respectively by the Southern 

 Party from the vicinity of the Beardmore Glacier 83° 50' to 85° 10' S. lat. ; the Western 

 Party from the Ferrar Glacier region, 78° S. lat., and the Magnetic Pole Party* from the 

 coast-line between 78° and 75° S. lat. The geological conditions over this region appear 

 to be very similar. For this and other reasons it is found advisable to tabulate under- 

 one scheme the specimens from all three sources. In most cases the specimens were 

 collected as erratics ; when otherwise the fact is expressly stated. 



THE SEDIMENTARY ROOKS 



Typical conglomerates, sandstones, slates, limestones, and even carbonaceous shales 

 and sandstones, as well as true coal, are exemplified. These argue water conditions 

 and a milder climate than now prevails in those latitudes. There are, nevertheless, 

 often present certain characters which indicate a severe and almost glacial climate. 

 The diagnosis of deposition under semi-glacial conditions lies in the intimate character 

 of the rocks as revealed by microscopic study and analysis. The thick arkose and 

 greywacke formations I regard as corresponding to such semi-glacial conditions. I 

 have arrived at this conclusion after a detailed study of the glacial and interglacial 

 sediments in Australia corresponding with the Cambrian and Pernio -Carboniferous 

 ice ages. ' Similar arkoses and grey wackes, as well as unleached muddy silts, invariably 

 accompany these tillite horizons, often repeated many times in waning sequence above 

 and below the latter. This recurrence indicates the continuance of strophic periods. 



Examples of true tillite are almost absent amongst the collection : these are limited 

 to several pieces of a recent character from the coastal moraines of McMurdo Sound, 

 and a scrap of an older-looking type from a moraine at sea-level near Mount Larsen. 



In the valleys inundated with summer waters in the Ferrar Glacier region there 

 is evidence that deposition of travertine is now taking place. Travertine is found 

 coating the pebbles and even cementing gravel to form a hard rock. 



The existing arid conditions, united with the fact that complete ablation of snow 

 and ice masses usually takes place before a melting temperature is reached, result in 

 the concentration of any contained dissolved salts. Thus residues of sodium, magnesium, 

 and lime sulphates and chlorides are of frequent occurrence. 



* The MS. of this paper was received by the General Editor in September 1911. Subsequently 

 Scott's Northern Party, in 1912, recovered the collection of rocks cached and unretrieved by us at 

 Depot Island. In my absence in Antarctica the Depot Island collection has been described by 

 Mr. L. Cotton and forms a further section of this volume. — D. M., January 1916. 



ii 203 2 G 



