ScHARFF — Some RenutrkH on the AUaittiii rrohlem. 277 



proWem, I i)ropose, in tlic following pages, to deal sliortly with the 

 geographical distribution of the principal groups of vertebrates and 

 invertebrates, iu so far as it affects the (luestions of the existence of a 

 former land-connection between the Old World and the Atlantic Islands, 

 and of a land-bridge across the mid- Atlantic. 



GrEOLOGY OF THE AtLAKTIC IsLANDS, 



Teneriffe, the principal island in the archipelago of tlie Canary 

 Islands, has always been a centre of attraction for the naturalist, on 

 account of the beauty of its scenery, and from the fact that it possesses 

 a volcano rising to an elevation of 12,000 feet. Not only its Zoology 

 and Botany have been carefully studied, but competent geologists 

 have from time to time visited it, and have given us many valuable 

 observations on the natui-e of the rocks found upon the island. 



Being entii'ely covered by immense masses of recent lava, no 

 fossiliferous deposits, if such do exist, have as yet been encountered, 

 the only indication of the presence of older crystalline rocks having 

 been obtained by blocks ejected from the Old Peak and other volcanic 

 vents. 



On the islands of Palma, Fuerteventura, and Gomera, an older 

 mountain-chain, consisting of diabase — an eruptive rock generally found 

 in older geological formations — has been shown to exist. Fritsch and 

 Beiss are of opinion that rocks of a similar nature also form the founda- 

 tion of the more recent volcanic deposits on Teneriffe (p. 315). 



On Grand Canary and Palma, two islands belonging to the Canary 

 group, an upheaval of from 600-1000 feet can be demonstrated; and in 

 Madeira, one up to nearly 1400 feet, while it is surmised that there was 

 probably a similar rise in Teneriffe. 



The Azores and the Canaries, as well as Madeira, are believed by 

 Fritsch and lleiss to be contemporaneous ; and these authors maintain 

 that, at the commencement of Middle Miocene times, a considerable 

 part of the mountain masses of the islands must already have been 

 formed (p. 220). 



Madeira differs from Teneriffe in so far as volcanic activity has 

 ceased for a considerable time past ; so that even the most recent 

 lavas exhibit signs of long erosion. Marine deposits occur here at 

 a considerable elevation as well as on the Azores, and on the islands 

 of Porto Santo and Gran Canaria ; and geologists seem to agree as to 

 these deposits having been laid down towards the middle of the 

 Miocene Period. 



Hartung, who specially studied the geology of Madeira, looked 



