82 I'KRCv qiens?:l 



rim in May 1923. l^aile\' Willis sa\'s: "In this sense and to this extent we 

 may consider San VcWx an active volcano" (26, p. 370). The Galapagos Islands 

 are still the seat of volcanic eruptions. As late as 1925 lava flows reached the 

 sea, {)()urin^ over the 1 00 foot cliffs (27, p. 9). The Juan Fernandez Islands 

 on the other hand show no signs of recent volcanic activity but, as recorded 

 above, one, and possibly, several sub-marine explosions have taken place in their 

 immediate vicinity during the past century. 



The formation of fissures in locating the position of the volcanic islands 

 bordering the South American continent may be conceived to be connected with 

 dislocations of the oceanic sub-stratum as an after-sway of displacements during 

 the formation of the continental mountain ranges. Time connections between 

 violent eartlujuakes on the continent and volcanic activity on some of the adjacent 

 islands are significant in this respect. 



However, much of what has been said regarding connections of the volcanic 

 islands of the Pacific, whether founded on petrological or petrographical similarities 

 or on geotectonic orientation, must still be considered as conjectural. For the 

 present, we must agree with Daly that "a glance at the larger aspects of Pacific 

 petrolog\- shows how pitifully slight is our knowledge of the island petrography. 

 Now is not the time for settled convictions. Now is the time for concerted, 

 persistant effort, leading to a thorough exploration of the Pacific archipelagos, 

 under the auspices of a single institution with a staff of cooperating observers" 

 (R. Daly, Petr()gra{)hy of the Pacific Islands. Bull. Geol. Soc. of America, 27, 1916, 

 P- 331)- 



Acknowledgements . 



The writer is indebted to Professor P. Ramdoiir, Heidelberg, and to Pro- 

 fessor S. (kWKI.ix and Dr W. Uytenp.ogaardt for friendly cooperation in deter- 

 mining the ore minerals. Professor Ramdohr has taken some photomicrographs 

 of the same and kindly put them at my disposal for reproduction. 



Dr (). Mki.i.is has helpfully co-operated in taking most of the other photo- 

 micrographs. The landsca[)e j)hotographs have kindly been put at my disposal by 

 Professor C". Skoi 1 si!KR(;. They are taken by him on his visits to the Juan 

 i'ernandez Islands in 1908 and 1917. 



A grant from the foundation Lars Mikrtas Mixnk is gratefully acknowledged. 



.Mineralogical Department, University of Stockholm, 

 March 1952. 



