286 SOUTH AMERICA— THE ANDES REGIONS. 



Submarine streams of petroleum are even carried seawards, and iridescent films of 

 oil are often seen glistening on the surface of the water. 



Along the seaboard follow other hilly groups separated either by fertile 

 alluvial valleys, or by ravines which cannot be cultivated for lack of fertilising 

 water. The Sierra de Paita, between the E-ios Achira and Piura, has an elevation 

 of scarcely 1,300 feet ; but farther south the coast range skirting the Sechura 

 desert attains a greater height in Mount Ilescas. The headland projecting from 

 this point north-westwards to Punta Aguja ("Needle Point ") is the most advanced 

 promontory of South America. 



North of Lima the coast range culminates in a conic height to which has been 

 given the name of Darwin (5,840 feet). Other less elevated groups dominate the 

 valley of the Rio Eimac and the Peruvian capital. South of the Eio Grande, 

 Mount Criterion rises to an altitude of about 5,800 feet, while near Islay the 

 coast range, limited by the Eio Vitor, has an extreme elevation of 3,350 feet. 



The whole of this seaboard is subject to frequent underground disturbances, 

 and Callao, after being destroyed in 1630, was again nearly ruined in 1746, when 

 a huge wave hurled the shipping in the roadstead over piers and quays, and on 

 retreating left hundreds of houses levelled with the ground. These convulsions 

 are associated by the geologist Suss with a deep movement of the rocks caused by 

 the subsidence of the cliffs along the coast in the abysses of the Pacific Ocean. 



But in any case the Peruvian seaboard presents some curious phenomena 

 which were formerly attributed either to an upheaval of the shore or to a retreat 

 of the marine waters. On the northern slopes of the island of San Lorenzo, 

 sheltering the roadstead of Callao, are seen a series of three terraces which, 

 although somewhat obliterated, Darwin recognised as old beaches covered with 

 shells of the contemporaneous epoch in various stages of preservation according to 

 the different heights of the upheaved terraces. The upper beach stands at 

 present 84 feet above the mean level of the ocean. These changes of level, 

 however, may have taken place in remote prehistoric times, while the shells 

 observed by the great naturalist may perhaps be the accumulated refuse of 

 kitchen-middens. 



The apparent marine erosions seen higher up on the cliffs have also by some 

 naturalists been referred to the action of certain lichens, causing the rocks to 

 gradually crumble away, and in the course of a few years excavating veritable 

 caverns. Mr. Nation, of Lima, informed Mr. John Ball that after twenty-five 

 years' study he was satisfied that the appearances are due to sub-aerial and not to 

 marine action. " The chief agent, in his opinion, is a cryptogamic plant growing 

 on the surface of the rock. During a great part of the year, when dense fogs 

 prevail at this elevation, the plant is in active vegetation. In the alternations of 

 relative dryness and dampness of the air the cells swell and mechanically remove 

 scales from the surface, which are seen to accumulate raj)idly in the course of a 

 single season. I am disposed to think that vicissitudes of temperature play a 

 great part in the disintegration of rock surfaces, and such action mustr be 

 increased by alternations of moisture and dryness which must occur where, during 



