170 A NATUKALIST ON THE " CHALLENGER." 



the above conclusion after his voyage with Capt. 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 sub- 

 sidence 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 " Challenger'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, f 



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

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

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



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

 Vol. I, p. 401, 403. London, Macmillan, 1876. 



The species of Phanerogamia and vascular cryptogams found in 

 Kerguelen's, Marion, and Heard islands, are enumerated in Prof. Oliver'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 Staff 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 off both islands ; 

 6 a.m. maximum 43° F., minimum 40 o, 5 ; sea-surface 40° to 41°. 



On December 26 the temperature at 10 a.m. was 37° *8 F. ; midday, 

 43° ; midnight, 42°. 



