208 PETROLOGY OF ROCK COLLECTIONS 



The abundance of microcline felspar, the strain features, and the presence of garnet 

 indicate an origin from acid igneous rocks metamorphosed prior to the period of sedi- 

 mentation represented by the arkose. The character of the garnet and its association 

 with the felspar is clear evidence that the garnet was developed secondarily in the 

 original gneiss at the expense of anorthite molecules of the felspars. The most important 

 contributor to the newer sediment, it appears, was an acid garnetiferous gneiss. The 

 unsorted character of the mineral constituents — the angular nature of the grains — and 

 the freedom from chemical decomj)osition are, I believe, evidence that disintegration 

 and deposition took place under semiglacial conditions. In small hand-specimens, 

 rocks of this character are difficult to distinguish from some dynamometamorphosed 

 granites, but I feel satisfied that there is no confusion in this case. Thick deposits 

 of a similar nature are regularly met with amongst the beds associated with glacial 

 horizons in South Australia. 



Other specimens from the Upper Glacial Depot, Beadmore Glacier, not otherwise 

 differing from this arkose type, carry abundant carbonaceous material along certain of 

 the bedding planes. Thus, finally, carbonaceous shale and grits are arrived at and 

 indeed coal* itself is amongst the specimens associated therewith. 



Though this arkose appears to be the prevailing psammite of the Beadmore Glacier 

 area there are, also, specimens more nearly approaching normal quartzites. One of 

 these from the Cloudmaker is a buff-coloured felspathic quartzite. Distinct and regular 

 bedding lines are marked out by iron-ore zones alternating with bands free from iron 

 ores. In it, current bedding is well shown. 



PELITES 



Examples of this class are rare amongst the collections. On the magnetic pole 

 journey only a few specimens of limestone and a few chips of slate were met with ; 

 amongst the former is an interesting erratic from Dunlop Island, the latter are mostly 

 from amongst the moraines in the vicinity of Mounts Larsen and Nansen. From the 

 Ferrar Glacier area Priestley collected fragments of a dense calcareous slate from the 

 upper moraines. This material in character recalls the non-fossiliferous Cambrian 

 slates of South Australia, with which I am familiar. 



In the Beardmore Glacier collection are a number of examples of slates and phyllites. 

 It is quite likely that all are of one age, as indicated by a specimen which clearly shows 

 that its phyllitic characters have been induced by the infiltration of mineral -bearing 

 waters along a fissure now occupied by vein quartz. Specimens from the vicinity of 

 the Cloudmaker range from a faintly purple-coloured slate to light grey or greenish 

 coloured phyllites in which abundant sericite has been developed ; minute particles 

 of pyrite are also frequent. In one case the phyllite is spotted and contains a pyrite 

 crystal 1 cm. square. The evidence of the quartz vein and the general metamorphism 

 of the slates argues a date of deposition antecedent to an igneous intrusive period 

 in the local geological history. It is unlikely that these sediments are newer than the 

 Palaeozoic. Associated with these slates and phyllites are calcareous types and even 

 pure limestones.f 



* The coal strata are described elsewhere in these volumes. 



f The limestones are elsewhere specially described by Professor E. W. Skeats. 



