308 TECTONIC GEOLOGY 



viz. peridotites, gabbros, pyroxenites, orthophyric trachytes, sanidinites, microti- 

 nites, camptonltes, and an orbicular augite syenite." The occurrence of these in- 

 clusions, he says, " gives some idea of the deep-seated rocks whose formation has 

 accompanied the eruption of the lavas." 



Professor W. G. Woolnough has, in his description in this Memoir of the erratics 

 of Cape Royds, discovered several old plutonic rocks distinctly alkaline in character, 

 so that this region was evidently alkaline in comparatively early geological times, 

 perhaps as far back as late Palceozoic. 



W. N. Benson, B.Sc, in his detailed description in this Memoir of the quartz- 

 dolerites of the Ross Region, has specially commented on the very close resemblance 

 of these to similar rocks forming the great sills of Tasmania, those of the Karoo of 

 Natal and Zululand in South Africa, of Venezuela, Northern Brazil, British Guiana, 

 the palisades of the Hudson River, &c. 



Dr. D. Mawson has given a petrological description in tliis Memoir of the chief 

 types of intrusive rocks met with in our expedition in South Victoria Land. He has 

 not attempted to touch on the question of whether or not they show Andean affinities. 

 Analyses of the typical granites from Cape Irizar show the rock to be very low in 

 lime and magnesia, and high in potash and soda, the former being in excess of the 

 latter. The granite near Mount Larsen, while still very poor in magnesia, contains 

 nearly 3 per cent, of lime and 7 per cent, of alkalies, the soda slightly in excess of 

 the potash. The intrusive dyke rocks of quartz- and felspar-porphyry from near 

 Mount Larsen are poor in lime and magnesia, and contain over 8 per cent, of alkalies, 

 the potash being in excess of the soda. The same feature is noticeable in the aplitic 

 granite porphyry of Cape Irizar, with the exception that in this case the soda is in 

 excess of the potash. This chemical composition of the older granites, granite 

 porphyries, and quartz- and felspar-porphyries, is widely different from that of the 

 Pacific type, and is essentially an Atlantic type of rock. On the other hand, the 

 kersantite lamprophyre from Cape Irizar contains nearly 6 J per cent, of lime and 

 about 5 J per cent, of soda and potash in the aggregate ; the rock thus approaches a 

 Pacific type. This rock shows a distinct relation to the sphene-bearing diorites ; the 

 latter contain over 7 per cent, of lime, and about 5i per cent, of alkalies. Thus the 

 rock is intermediate between Pacific and Atlantic types. In their frequent large 

 homogeneous inclusions of basic rocks, the gneissic granites, like those of Depot 

 Island, resemble the granodiorites of the Andes. In the presence of micropegmatite 

 and nearly uniaxial enstatite-augites the granophyric quartz-dolerite sills of South 

 Victoria Land show a great resemblance to the Konga type of diabase so well known 

 in Sweden. 



As already stated, the quartz-dolerites of South Victoria Land, with their inter- 

 stitial granophyric patches, are petrologically so extremely like the dolerite sills of 

 Tasmania, that it is highly probable that the intrusions in these two widely sejjarated 

 countries were synchronous. 



