SUPPLEMENTARY NOTE A. 117 



lilies, sequoias, swamp-cypresses (Taxodium), &c. of extinct 

 species, and varieties of known species now living in temperate 

 latitudes, and doubtless acclimated to arctic conditions. The 

 adaptive constitution of plants has not been sufficiently considered 

 in connexion with this question. 



I shall conclude with a few brief remarks on linear igneous 

 disturbances. Admitting the existence of a number which may 

 be included in the equatorial system of jointing, disturbances of 

 the kind are for the most part limited to the meridional zones 

 of weakness. As is well known, a most important series of 

 volcanoes characterizes the western borders of the two Americas ; 

 and a similar series lies off the east coasts of Asia, belonging, 

 in my opinion, one to the west-of-north and the other to the 

 east-of-north section of meridional jointing : both series become 

 united in Behring's Sea. Other writers, by connecting the equa- 

 torial series of volcanoes north of Australia with the above two, 

 have constructed a " circle of fire ;" but with far too limited a 

 range. The two meridional series (by pursuing a direct course, 

 so as to embrace the Cocos Islands, St. Paul's, Kerguelen's Land, 

 Enderby's Land, thence curving to Trinity Land, passing on to 

 the South Shetlands, and through Fuegia into the Patagonian 

 Andes) form but one a great volcanic girdle, which may be said 

 to stretch without interruption round the world, traversing the 

 Arctic regions a few degrees east of the North Pole, and inter- 

 secting the Antarctic circle at a corresponding distance west of 

 the South Pole thus dividing the crust of the globe along its 

 greatest zones of weakness into two nearly equal halves, and at 

 the same time separating its superficies into a water- and a land- 

 hemisphere. 



As to reflections which may naturally arise in connexion with 

 the last subject, I avow myself to be, scientifically, too much of 

 a teleoptimist, too extravagant a timist, and too little of a 

 catastrophist to entertain any that involve serious or disquieting 

 apprehensions. 



