304 TECTONIC GEOLOGY 



Nevada of California, Yellowstone National Park, Vancouver, and even certain 

 iDarticular granites in Alaska. One meets with almost similar rocks in the Lesser 

 Antilles. This is the largest petrographical province in the world. This similarity- 

 was fii-st emphasized by Dr. O. Nordenskjold. Nordenskjold specially studied the 

 acid types, which are more of the nature of plagioclase granites than orthoclase 

 diorites, and he has no doubt that the soda in these rocks predominates over potash. 

 He considers these rocks to bear a close resemblance to those of Tierra del Fuego 

 and Patagonia. 



M. Gourdon (oj). cit., pp. 206-7) states that he has compared the rocks of the 

 Charcot Expedition of 1903-5 with those collected at Cape Horn by Dr. Hyades in 

 1883, and finds the closest resemblance between the two groups. Quartziferous 

 diorites, showing uralisation phenomena, are equally characteristic of both areas, but 

 the predominance of zoned plagioclase is the most striking characteristic possessed 

 by both groups of rock in common. Gourdon states that the Antarctic rocks are 

 clearly granular, showing no tendency to develop into microgranular types, nor in 

 the direction of the ophitic structure found in types poor in quartz. The microlitic 

 rocks, according to Gourdon, can be divided into two groups ; the one comprising 

 very much older rocks is probably very old, the other, on the contrary, is remarkably 

 fresh, and is certainly of volcanic origin. Although no trace of any volcano was 

 observed by the French Expedition of 1903-5, Gourdon has no doubt whatever that 

 these volcanic rocks are of recent age. He emphasizes the fact that Deception Island 

 still shows traces of activity in the form of fumaroles, hot springs, &c., and Bridgman 

 Island, an intermittently active volcano, may of course be included here. He also 

 recalls that on the north-east of Terre Louis Philippe there are evidences of modern 

 volcanic activity in Paulet Island and Mount Lindenburg. Gourdon's last j^aragraph 

 is so important that we may be permitted to quote it in full (oj). cit., p. 208) : — 



" Enfin la decouverte, parmi les blocs errants de I'ile Wandel, d'un microgranite 

 alcalin a amphibole et pyroxene sodiques, pose une question nouvelle. 



"Les caracteristiqiies chimiques et mineralogiques de cette roche sont, en eftet, 

 tout a fait opposees a celles des autres roches eruptives de la region ; elle est presque 

 totalement depourvue de chaus et tres riche en alcalis. Ne serait-elle pas I'indice de 

 I'existence jilus au sud d'une province petrographique nouvelle et, dans le cas ou 

 elle serait indigene, ne constitue-t-elle qu'une exception dont il serait en tout cas 

 interessant, au point de vue theorique, de preciser la portee? C'est ce que je 

 vais m'efforcer d'elucider au cours de I'expedition nouvelle qui va j^arter dans 

 quelques mois." 



Dr. Alfred Harker in his work, "The Natural History of Igneous Rocks" * (p. 91), 



* Atlantic. Pacific. 



Alkali-felspars form a large proportion of the Alkali-felspars not abundant except in the more 

 more acid and intermediate rocks, and occui' acid rocks, and wanting in the basic ; soda- 



in many rocks of low acidity. lime-felspars abundant. 



