ADDITIONAL COMMENTS ON THE GEOLOGY OF THE JUAN FERNANDEZ ISLANDS 4! 



Fig. I. Perspective view of Masafuera from the East. (Reproduced from F. Johow, Estudios sobre 

 la flora de las Islas de Juan Fernandez. Santiago de Chile 1896.; 



Masafuera presents notable dissimilarities to Masatierra. Its dome-shaped, 

 sharply bounded outline with an approximately oval circumference and its impos- 

 ing height give an impression of a volcanic configuration deviating from that 

 of Masatierra. On the west side of the island the cliffs fall all but perpendicularly 

 for over i ooo m. The shore line below is a stony and sandy reach, in part 

 named Loberia vieja on account of the number of fur seals found there at certain 

 seasons. The eastern coastline has a very different appearance. As the highest 

 ridge lies towards the west, the fall on this side is not so precipitous. Instead 

 it is traversed by numerous narrow and steep sub-parallel erosion valleys (que- 

 bradas). Attempts to ascend the higher parts of the island can only be made from 

 the eastern side by means of these quebradas, a climb which is anything but 

 easy going (Fig. 3). The highest peak is i 500 m. 



The sketch in Fig. i gives an excellent conception of the singular configura- 

 tion of Masafuera's eastern escarpments. 



The Juan Fernandez Islands are exclusively formed of volcanic material, in 

 many respects of much the same nature as in other volcanic islands of the 

 eastern Pacific, All indications tend to show that they are of late origin. Both 

 VON Wolf (15, 1929, p. 771) and J. BrCggen (16, p, 59) consider them to be 

 late tertiary or pleistocene in age. Lacroix says regarding all the non-coral- 

 line islands of the southern central Pacific: "leur age precis est indetermine, 

 mais il est certainement tertiaire, pleistocene ou meme, dans certains cas, recent" 



(14, P- 55)- 



No signs of recent activity have been found on the Juan Fernandez Islands. 

 That the immediate environs have recently been subjected to sub-marine volcanic 

 activity is, however, evident from a narrative, published in the Report of the 

 Challenger F:xpedition as follows: "In 1835 Masatierra appears to have been 

 governed by a Mr SUTCLIFFE, an Englishman in Chilean service. He was present 

 when the earth-quake took place on the 20th of February of that year, of which 

 he gives the following account: At 11.30 a.m. the sea rose over the mole and 

 afterwards retired, leaving the greater part of Cumberland Bay dry, so much so 

 that old anchors on the bottom became clearly visible. The earth then began to 

 shake violently, and a tremendous explosion was heard, the sea still receding 

 in immense rollers, which afterwards returned, violently rising to such a height 

 that the settlement was literally covered and washed away, when the sea again 

 receded. The phenomenon occurr-ed four times, causing much destruction, uproot- 

 ing trees and drowning cattle. Shortly after the explosion, a large column, some- 



