5^8 Mr. D. A. Bannermau on the [Ibis, 



Review of the Ornis. — General Conclusions. 

 Having now completed tlie List of Birds of the Canai'y 

 Islands and dealt at length with the migratory species, I 

 propose to discuss some of the problems which the Ornis of 

 the Archipelago snggusts, especially as regards the distri- 

 bution and affinities of the birds found therein and their 

 bearing on the formation of the islands. 



Geological Formation and Age of the Canary 

 Archipelago. 



Several theories have been advanced to explain the origin 

 of the islands. It has been suggested that they are the 

 remaining peaks of a sunken Atlantis Aviiich lias long since 

 been swallowed up in this region, or that the islands were 

 formerly joined to the nniinland of Africa, or again that they 

 are merely " of volcanic origin. '^ The evidence of geologists 

 certainly points to the last explanation as the correct one. 



Thanks to the famous voyages of the ' Challenger,' 

 ' Michael Sars,' and other less celebrated ocean survey 

 ships, the bed of the ocean west of Morocco is comparatively 

 well known, mid we are thus able to review this region with 

 a certain amount of confidence. A glance at any recent 

 map of the Atlantic Ocean reveals the fact that an enormous 

 trough of great de[)th runs parallel with the West African 

 coast-line, and is separated from a similar trough on the 

 western side of the Atlantic by a gigantic submarine ridge. 

 Glancing at the chart of the Eastern Atlantic we are struck 

 by the fact that a long chain of islands lies on this sulnnarine 

 ridge or else between it and the African coast — the Azores, 

 Porto Santo, Baixo Island, the Madeira Group, the Salvages 

 and the Pitons, the Canaries, the Cape Verde Islands, St. 

 Helena, Ascension, the Tristan da Cunha Group, and Gough 

 Island. With tiie exception of two islands (Santa Maria 

 and Majo) all these islands are mainly built up of volcanic 

 rocks. Anyone who has travelled thi-ough the Canary Islands, 

 particularly those of the eastern group, cannot but be struck 

 by the volcanic nature of the ground. Evidence of terrible 

 upheavals is to be seen on all sides — perfectly formed craters, 



