ADDITIONAL COMMENTS ON THE GEOLOGY OF THE JUAN FERNANDEZ ISLANDS 75 



Other respect between the Juan Fernandez Islands and the volcanic islands of the 

 eastern Pacific. Some quotations may be given. 



Charles Darwin already expressed views regarding geotectonic connections 

 between the Juan Fernandez Islands and, on the one side, the South American 

 continent, on the other, the Galapagos Islands. In his 'Observations on the 

 volcanic islands and parts of South America' he says: "Some authors have 

 remarked that volcanic islands occur scattered, though at very unequal distances, 

 along the shores of the great continents, as if in some measure connected with 

 them. In the case of Juan Fernandez, situated 330 miles from the coast of Chile, 

 there was undoubtedly a connection between the volcanic forces acting under 

 this island and under the continent as was shown during the earthquake of 1835, 

 The islands, moreover, of some of the small volcanic groups, which border the 

 continents, are placed in lines, related to those along which the adjoining shores 

 of the continent trend; I may instance the lines of intersection at the Gala- 

 pagos" (20, p. 144). 



In his paper 'Constitution lithologique des lies volcaniques de la Polynesie 

 Australe' Lacroix gives expression to much the same trend of thought when 

 he writes: "Particulierement interessantes sont les iles volcaniques qui se trouvent 

 a une plus ou moins distance de I'Amerique du Sud, les iles Juan Fernandez, 

 San Felix et San Ambrosio, et enfin Galapagos, puis au large de I'Amerique 

 centrale, I'ile Clipperton. Bien que la connaissance de la lithologie de ces iles 

 soit loin d'etre completement eclaircie, on peut a present assurer que leur laves 

 different de celles des Cordilleres des Andes, c'est-a-dire de la serie circumpacifique 

 et montrer qu'elles se rattachent a la serie intrapacifique" (14, p. 64). 



In 'La Face de la Terre' Emmanuel de Margerie refers to the same 

 subject as follows: "Le Relay de la marine des Etats-Unis a signale, au large 

 de Valparaiso 5.651 metres. A I'ouest de ces fosses sont situees les deux iles 

 volcaniques anciennes de San Felix et San Ambrosio; au Sud de ces iles le 

 croiseur Chilien Presidente Pinto a trouve, sur une etendue de 760 km, des 

 profondeurs si faibles qu'il est probable qu'une crete sous-marine, orientee a 

 peu pres N — S, s'allonge dans la direction de I'ile Juan Fernandez" (25, III, 



P-I359)- 



In his 'Description and Geology' of San Felix and San Ambrosio, Bailev 

 Willis writes: "San Felix and San Ambrosio are volcanic islands in the South 

 Pacific Ocean, San Felix being situated in latitude 26°: 5' south and longitude 80°;' 

 west of Greenwich and San Ambrosio lying about 16 km to the east-south-east. 

 They are about 500 miles west of Chanaral on the east coast of Chile, and the 

 same distance due north of the group of Juan Fernandez and Mas-a-fuera. The 

 South Pacific charts show several rocks or islets and some whose existence is 

 recorded as doubtful, which, with the above-named islands, form an archipelago 

 strewn on a narrow submarine ridge that extends along the meridian ol 80 

 degrees west from about 36 degrees south to 26 degrees south, the ridge being 

 defined by the 2.000-meter contour line. Knowing that all these islands and 

 islets are peaks of volcanoes, we may suspect that there are more of them than 

 we can see; but this must remain an unverified guess until detailed soundings 



