152 J. C. Branner — Geology of Fernando de Noronha. 



side. The rocks of the summit are rudely columnar as is shown 

 in the accompanying cut. The ledge just northwest of the 

 Horta do Pico, fig. 3, shows the columnar structure of phono- 

 lite better perhaps than any other exposure upon the island. 

 In most of these phonolites the metallic sound produced by 

 striking with a hammer is very marked, especially when a 

 somewhat thin slab is separated from the mass. From this 

 peculiarity the Brazilians frequently call this rock " pedra de 

 toque," which is the equivalent of our word " clinkstone." 



The Peak is the most striking landmark in the South Atlan- 

 tic ocean ; it is 1000 feet high,* with the upper portion per- 

 pendicular or overhanging in such a manner as to make the 

 summit quite inaccessible. The few drawings of this peak that 

 have been published are taken from the same point — the 

 anchorage — and even the best of them, that in the Challenger 

 reports, conveys but a poor idea of its grandeur. Seen from 

 other points it presents a striking variety of outlines. 



It would be interesting to know whether this peak had un- 

 dergone any marked changes since the discovery of the island 

 in 1503, but unfortunately we have no detailed description of 

 it as it appeared at that time, and the oldest drawing, that 

 made by Ulloa in 1745, is clearly too imperfect to be trust- 

 worthy. It is evident, however, to one on the ground, that it 

 is being slowly thrown down under the combined influence of 

 sun and rain and the daily changes of temperature. Climbing 

 up the accumulation of talus that slopes down from the base of 

 the solid part of the peak to the seashore, it is noticeable that 

 this material, loose as it is, stands at an angle of unstable equi- 

 librium, and when disturbed in any way, miniature avalanches 

 of loose stones slide down the slope, sometimes a hundred feet 

 or more. Wherever this debris is stable there is sufficient soil 

 upon it to support vegetation ; and it is thus covered here and 

 there with small tomato plants that have escaped from cultiva- 

 tion. In many places it was noticed that these plants were 

 freshly broken and bruised by fragments that had fallen from 

 the peak above. 



From top to bottom two great joints divide the Peak into 

 three vertical sections. Into these crevices fall fragments of 

 stone, which, heated and expanded during the day by the pow- 

 erful rays of the sun, and cooled and contracted by the cool rains, 

 or at night by radiation, wedge themselves deeper and deeper 

 into the crevices and thus push off pieces large and small. 

 Some years ago, no one seemed to know how many, the little 

 fort near the base of the peak was almost completely demol- 

 ished by a great mass of rock that fell from the Peak and rolled 



*My own triangiilation makes its height above tide 332 meters. Houchez 

 gives it at 305 meters. 



