272 Tvoceedincjs of the Royal Irish Academij. 



volcanic rocks ; secondly, that they were surrounded hy gi-eat depths 

 of water; and, lastly, that they possessed no indigenous land- 

 mammalia. 



As regards the fact that the Atlantic Islands are composed o£ 

 volcanic rocks, it does not necessarily imply that they could not, 

 therefore, have formed part of the continent of Europe in former 

 times ; for even Hartung, who made a special study of the Geology of 

 Madeira, looked upon the Atlantic Islands as the summits of sub- 

 merged mountain-chains (p. 175) ; while two other geologists — viz., 

 Guppy (p. 496) and JS'eumayr (p. 547) — maintain that these islands 

 are the remnants of a great continent which united the Old World 

 with the New. Lyell, ou the other hand, arguing from the supposed 

 great depth separating the Atlantic Islands from the Continent, does 

 not consider it possible that they could have been connected with 

 Euroi)e (p. 411). However, as Dr. Blanford reminds us, in his 

 interesting address to the Geological Society of London (p. 34) : " The 

 occuiTenee of volcanic islands does not prove that the area in which 

 they occur is not a sunken continent." " If," he continues, "Africa 

 south of tlie Atlas subsided 2000 fathoms, what would remain above 

 water? So far as our present knowledge goes, the remaining islands 

 would consist of four volcanic peaks — the Camaroons, Mount Kenia, 

 Kilimanjaro, and Stanley's last discovery, Euwenzori, together with 

 an island, or more than one, containing part of the Abyssinian table- 

 land, which, like the others, would be entirely composed of volcanic 

 rocks." 



Dr. "S\''allace's second statement, that the Atlantic Islands were 

 surrounded by great depths, is only partially correct. On the little 

 map he published in 1900 (A, p 253), Dr. Wallace indicates a depth of 

 12,000 foet between Madeira and Europe, though it is now twenty- 

 five years since Commander Gorringe, of the United States' jN'avy, 

 discovered the Gettysburg Bank, and demonstrated the undoubted 

 fact that there are shallow banks only a couple of hundred feet below 

 the surface of the sea in that area. He also suggested that a sub- 

 marine ridge probably connected the island of Madeira with the 

 coast of Portugal {cf. J. J. Wild, p. 377). 



Tlie Azores seem to be separated bymuch greater depths from tlie Con- 

 tinent ; and Dr. Wallace is so convinced of the permanence of the great 

 ocean basins that he will not allow that any very great changes of level 

 have taken place in fonner times. But that Dr. Wallace's views are 

 not generally accepted may be gathered from the remark made by 

 Dr. Blanford that " not only is there clear proof that some land-areas 



