AND THE WKST INDIAN ERUPTIONS OF 1902. 



227 



epoch (which was one of great elevation of the sea-bed and land) hy 

 which the two continents were joined, and l)y means of which land 

 animals migrated from one continent to the other, and finally he 

 points out the connection lietween the oscillations of level and the 

 outbursts or subsidence of volcanic activity. 



Professor Logan Lobley, while i-eferring to the AVest Indian 

 volcanoes, deals with the source and origin of volcanic action on 

 broad principles, which can scarcely be gainsaid. By his work on 

 Jfount Fesuvius, and his numerous papers in scientific publications, 

 he has taken a high place amongst authorities on vulcanicity, and I 

 quite agree with him that the central-source theory is untenable. I 

 do not think, however, that he sufficiently recognizes the necessarily 

 distinctive sources of the heavy basic, and the lighter acid, lavas as 

 originally determined by Durocher, nor does he account for the 

 sequence of these varieties of lava at apparently the same source as 

 in the case of the Siebengeberge in the Ehine Valley, where the 

 light acid trachyte was succeeded by the basic basalt lava. These, 

 however, are minor points, and do not detract from the intrinsic 

 value of the essay, and they may not have come within the scope of 

 his communication. 



