Chap. vii.J FORMER CONTINUITY OF LAND. 147 



Pri/jgka could have been transported from one island to 

 another by birds ; they seem to be remarkably perishable ; 

 besides, the distinctness of the genus points to a former wide 

 extent of land on which its progenitors became developed. 

 The existence of fossil tree-trunks in Kerguelen's Land points 

 to similar conditions. Sir J. D. Hooker, in the "Flora 

 Antarctica," p. 220, expressed the above conclusion after his 

 voyage with Captain Ross, 35 years ago, and with singular 

 foresight suggested that there has taken place " the destruction 

 of a large body of land, of which St. Paul's and Amsterdam 

 Island may be the only remains ; or the subsidence of a chain 

 of mountains running east and west, of which Prince Edward 

 Island, Marion and the Crozets are the exposed peaks." This 

 view is directly confirmed by the discovery by the " Chal- 

 lenger's " soundings of the Kerguelen Plateau, which " rises in 

 many parts to within 1,500 fathoms of the sea surface, and 

 forms the common foundation of all the islands situated in 

 this part of the world, viz.. Prince Edward's Islands, the 

 Crozet Islands, the Kerguelen Group, the Heard Islands, and 

 the islands of St. Paul and Amsterdam," " as proved by the 

 soundings of both the ' Challenger ' and the ' Gazelle.' "* The 

 occurrence with the cabbage on Heard Island of the helpless 

 wingless fly, seems a further proof that the plant was not 

 conveyed to the various islands by birds. It is hardly possible 

 that both could have been transported. The fly could 

 probably not exist without the cabbage. The existence of the 

 same species of fresh water fish in New Zealand, Tasmania, 

 the Falkland Islands and South America, points also to the 

 former existence of more intervening land between these 

 points. t 



* " Thalassa," an Essay on the Depth, Temperature and Currents of 

 the Ocean, by J. J. Wild, of the Civilian Scientific StaiT of H.M.S. 

 "Challenger,'" pp. 19 and 23. London, Marcus Ward, 1877. 



f A. R. Wallace, "The Geographical Distribution of Animals," Vol. I., 

 pp.401, 403. London, Macmillan, 1876. 



The species of Phanerogamia and vascular cryptogams found in 

 Kerguelen's, Marion, and Heard Islands, are enumerated in Prof. Olive] s 

 report upon my collection, " Journ. Linn. Soc," XIV., p. 389, from which 

 report the specific names above cited are taken. For the Cryptogamia 

 of Marion Island, vide list of papers at the end of this book. 



The following are the temperature-observations taken on board the 

 "Challenger " by Stafi" Commander Tizard, R.N.: — 



On December 26th, when the ship was off Marion Island, the ther- 

 mometer, read at six in the evening, showed for the preceding twelve 

 hours, maximum 45°'5 F, minimum 36°-2. 



December 27th. The ship was occupied dredging oft" both islands ; 

 6 A.M. maximum 43° F., minimum 40°"5 ; sea-surface 40° to 41°. 



On December 26th the temperature at 10 a.m. was 37°' 8 F. ; middaj', 

 43° ; midnight, 42^ 



