ORIGINAL ARTICLES. 



The Geology of Ascension and St. Helena Islands. 



By Reginald A. Daly, Harvard University, Cambridge, 

 Massachusetts, U.S.A. 



rpHE writings of Charles Darwin, Renard, Mellis, Reinisch, and 

 -^ others have already made the salient features of lonely 

 Ascension and St. Helena accessible, if not familiar, to geologists — 

 St. Helena has won the surprised interest of biologists, who have 

 long speculated on the origin of its unique species of plants and 

 animals. From each island collections of rocks have been made. 

 Following Renard's well-known contribution to the petrography of 

 Ascension (" Challenger " Reports, Physics and Chemistry, vol. ii, 

 1889), Reinisch's paper in the Report of the Deutsche Siidpolar 

 Expedition (1901-3) gives a large number of petrographical 

 descriptions, including a goodly number of chemical analyses. No 

 adequate geological map of either island has, however, been 

 published, nor, indeed, was this really possible before the British 

 Admiralty had issued the greatly improved chart (No. 1691) of 

 Ascension, in 1910, with corrections added to the year 1921, and the 

 British War Office had issued its excellent contour-map of St. Helena, 

 dated 1904. Each map is on a large scale. Even, though lacking 

 contour lines, the Ascension chart was obviously to be of service to 

 anyone attempting a reconnaisance survey of that island. 



As a member of the Shaler Memorial Expedition, sent by Harvard 

 University to * carry out geological investigations in the South 

 Atlantic and in South Africa during 1921-2, the writer has been 

 privileged to complete a reconnaissance map of each island, and 

 thus make more definite the available information. Since it will 

 be long before maps and full reports can be published, a summary is 

 herewith presented. This account will be best followed if read 

 alongside of the topographic maps mentioned. 



It is a pleasure to record the many courtesies extended by the 

 Admiralty officials, who alone conld give permission to land on 

 " His Majesty's Island, Ascension ", and those extended by the 

 officials of the Colonial Office, both in London and St. Helena. 

 Special acknowledgment must be made of the efficient, generous 

 help of Major C. A. Tennyson, Naval Commandant of Ascension, and 

 of his staff, as well as similar aid given by Governor R. F. Peel, of 

 St. Helena, and his staff. 0th ei valued privileges were extended by 

 officers of the Eastern Telegraph Company, and of the comfortable 

 steamships of the Union-Castle line. 



Ascension. 

 The 38 square miles of Ascension are almost treeless. Except 

 on a few young lava-fields and over some rugged ground in the 

 eastern part of the island, travel is easy. The summer climate. 



