PETROGRAPHICAL EVIDENCE 303 



2. Petrograpliical Character of the Eruptive Rocks. 



Petrographically Dr. G. T. Prior concludes that the volcanic rocks of Victoria 

 Land " belong undoubtedly to the Atlantic group," while the late Dr. E. Philippi of 

 the Gauss Expedition held that the coast of South Victoria Land is really of 

 Atlantic type. Dr. Otto Nordenskjold, J. Gunnar Andersson, Dr. J. Charcot, 

 E. Gourdon, and Arctowski are confident that Andean petrographical types ai"e 

 represented on the east coast of Graham Land. Gourdon * concludes that in the 

 area examined by the French Antarctic Expedition of 1903-5, under the command 

 of Dr. Jean Charcot, the whole area is occupied almost entirely by eruptive rocks, 

 amongst which granitoid types greatly predominate. The group of these granitoid 

 rocks forms a very homogeneous petrograj^hical series, ranging as it does from 

 granites to gabbros. He states that the continuity of the series is particularly clear 

 in regard to the granites and the quartz-bearing diorites. Their community of 

 origin is further emphasized by the character of the homogeneous basic enclosures 

 which both contain in abundance. Both in chemical composition as well as in 

 mineralogical characters these rocks are distinguished by certain clear characteristics. 

 From acid granites to basic gabbros the series is characterised by the abundance of 

 lime-soda felspars showing idiomorphic outlines, and as a rule well zoned. In the 

 most acid varieties of granite the plagioclases always predominate over the ortho- 

 clase, a natural result from the poverty of the magma in potash and its richness in 

 lime. Charcot after emphasizing these points remarks that these granites approach 

 the monzonites. He adds that the ferro-magnesian constituent most widely dis- 

 tributed is green hornblende, almost always accompanied by biotite, and some- 

 times associated with jsyroxene. 



Arjtowski,"!" in his observations on the rocks collected in Gerlache Strait by the 

 Belgica Expedition, considers it probable that these rocks resemble those obtained by 

 the French Expedition. Dr. Otto Nordenskjold and J. Gunnar Andersson conclude 

 that the chains of mountains along the western coast of Terre Louis Philippe are 

 formed of the .same series of granular eruptive rocks exhibiting the same characters. 

 Gourdon considers that, from the mineralogical point of view, the eruptive rocks of 

 this quarter of the Antarctic constitute a family having general resemblances to one 

 another in all their types, ranging from acid to basic, from volcanic to hypabyssal and 

 to plutonic. He considers, therefore, that the American side of the Antarctic contains 

 practically a well-defined petrographical province. This, he holds, shows a com- 

 munity of origin with that of the Andes of South America ; and it is also related, 

 m his opinion, to the dioritic rocks of the Cordillera of North America, the Sierra 



* Expedition Antarctique Fran9aise (1903-5). Dr. Jean Charcot. Geographic Physique, 

 Glaciologie, Petrographie, by E. Gourtlon, pp. 204-208. 



I H. Arftowski, Geographic Physique de la region Antarctique visite par I'expedition de \a, 

 Belgica (Bull. Soc. Beige de Geographic, No. 1, 1900), pp. 40-42. 



