T. Mellard Reade — The Island of South Georgia. 225 



V. — The Island of South Geoegia. 

 Ey T. Mellard Reade, F.G.S. 



THE German Expedition to South Georgia has brought back the 

 interesting information that this island, situated in the Antarctic 

 Ocean, Lat. 54° S., Long. 37° W., is composed of clay-slate.^ Not 

 only the part the membei's of the expedition were able to inspect 

 was found to be composed of this slate-rock, but the glaciers brought 

 down the same rock from the central portion of the island. In some 

 places the slate was interspersed with varieties of quartz. No 

 metals were found, but the rock contained a little iron, a quantity 

 insufficient to affect the magnetic needle. 



It has been stated, and in fact generally thought, that the whole of 

 the oceanic islands were composed of igneous rocks ; and principally 

 on this slender foundation of negative evidence has been erected 

 an immense superstructure of theory as to what is termed the 

 " Permanence of Oceans and Continents." 



The term Oceanic Island is rather an arbitrary one, and, by what 

 seems to me to be reasoning in a circle, those islands which, like 

 New Zealand, though surrounded with deep water, and far from any 

 other land, happen to be composed largely of sedimentary rocks are 

 denied an oceanic character, and are annexed as outliers to the nearest 

 continent. Thus islands are made to do double duty : first, to show 

 us, by the absence of sedimentary rocks, that the ocean is -'permanent " ; 

 and secondly, if sedimentary strata be present, to prove that they are 

 children of the land, and not of the sea. The obvious reply to this 

 is, that the igneous nature of peaks rising from the ocean is no 

 proof that the strata they rest on is non-sedimentary; whereas, on 

 the contrary, the sedimentary character of the rocks of an island 

 is a proof that there exists in the sea-bed about, an extension of 

 rocks of a similar nature. 



The case of the island of South Georgia will, however, be difficult 

 to meet, though I should not be much surprised to hear its oceanic 

 character denied by parity of reasoning. I find by measurement on 

 my map that it is not less than 1200 miles from the nearest continent, 

 viz. South America, and about 800 miles from the Falkland Islands. 

 It is also about one-third of the way between Cape Horn and the 

 Cape of Good Hope. The " Challenger " soundings did not come as 

 far south as this island, but directly to the northward stretches a 

 tongue of the Antarctic Ocean, with soundings of 2900 fathoms. 

 Although the soundings extend only to the 40th parallel, there are 

 certain indications, derived from the currents and the deep-sea tem- 

 perature, that an area of depression extends from the Falkland 

 Islands to the meridian of the Cape of Good Hope.^ 



Whether we label the island of South Georgia " Oceanic " or not, 

 the fact remains, that it is much further from any continent than the 

 Azores, St. Paul's Eocks, or Ascension, and about the same distance 

 from South America as is Tristan da Cunha from Africa ; and all these 



1 Nature, March 27, 1884, p. 509. 2 Thalassa, p. 18. 



DECADE III. — TOL. I. — NO. V. 15 



