LINNKAN SOCIETY OF LONDOX. 21 



least in the case of the tortoise aud of some of the birds, may 

 hereafter prove to be ouly well-marked races ; but this would 

 be of equally great interest to the philosophical naturalist." 

 Dr. Baur lays particular stress upon this condition, to which he 

 applies the term " liarmonic distribution," maintaining that sucli 

 a distribution could uever have come about by the accidental 

 arrival of a miscellaneous set of plants and animals, of some on 

 this, of others on another island, and that it can be only explained 

 by, and therefore proves, the formation of the islands by sub- 

 sidence of their common base. They are the tops of the volcanic 

 mountains elevated on a large and continuous mass of land * which 

 is now submerged below the water, but which probably in the 

 Ei'cene period, and possibly a little later, was still in connection 

 with the continent, possibly in the direction of the great Mexican 

 and Sonorau province. At the time when the islands were still 

 connected, the number of species inhabiting the district was 

 small ; when they became separated, " through isolation the 

 peculiar specialization of the species began: an originally single 

 species was differentiated in many different forms ; every island 

 developed its peculiar race."t 



Professor Alex. Agassiz (30) has severely criticised Dr. Baur's 

 view, on the ground ttiat it is entircjly opposed to geological 

 evidence. Separated from the mainland east and northw-ards 

 by a broad plain, declining in the deepest parts to 1500 

 and 2000 fathoms, without an intervening series of shallower 

 soundings or islands in the direction of the supposed former con- 

 nection with America, the Arcliipelago shows no trace of archaic 

 rocks, and, moreover, the petrographic character of its volcanoes 

 is basaltic, thus differing from the volcanoes of the mainland, 

 w hich are made up of trachytic and andesian material. Suess +, 

 in alluding to the divergence of opinion as regards kienozoic 

 changes of land and w'ater, considers biological facts to be of but 

 secondary importance, and therefore would lend the weight of his 

 authority to the opinion of Agas^iz. 



Yet the position taken up by Dr. Baur need not be abandoned 

 as hopeless, in spite of the absence of direct geological evidence. 

 Tlie biologist now and then may give a helping hand to the 

 geologist. 



The analogy between the Galapagos and Eastern Gigantic 



* Mr. Blanford concurs with Prof. Bouney that the occurrence cf volcanic 

 islands does not prove that the area in which they occur is not a sunken con- 

 tinent. " If Africa south of the AtUvs subsided liUUU fathoms, what would 

 remain above water? Si> far as our present knowledge goes, the remaining 

 islands would consist of four volcanic peaks — Camaroons, Kenia, Kilimanjaro, 

 and Kuweuzori, — together with an island " etc. (.\nniv. Address Geol. Soc. 18'.)0, 

 p. 34). Tliis same idea is expressed by Dr. Baur (1891, p. 307) tlius : — '• If 

 Lientral America should disappear by-and-by througli subsidence, the result 

 would be that the tops of the highest mountaius would form voicauic islands, 

 Bome with still active volcanoes." 

 t 22. p. 3U8. 

 I AntiiU d. Erde, i. p. 530. 



