IXXIV PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



western side of the continent during the pleistocene period ; that they 

 were unequal in amount at different parts of the coast ; and that the 

 action of the subterranean force was intermittent, periods of rest in- 

 tervening. Shells of the same species as are now hving in the shallow 

 waters of the shores of the Pacific, and in the same proportions as to 

 numbers, are met with in the island of Chiloe at a height of 350 feet 

 above the sea, near Concepcion at 625, and even, according to Lieut. 

 Belcher, at a height which he estimated to be 1000 feet. They 

 occur at the latter height near Valparaiso, and although diminished 

 in number, Mr. Darwin found four species in the same locality at an 

 elevation of 1300 feet. "These upraised marine remains occur at 

 intervals, and in some parts almost continuously, from lat. 45° 35' to 

 12° S. along the shores of the Pacific, a distance in a north and 

 south line of 2075 geographical miles ; and from the similarity in the 

 form of the country near Lima, it is probable they occur there also, 

 which would extend the line to 2480 miles. From the steepness of 

 the land on this side of the continent, shells have rarely been found 

 at greater distances inland than from two to three leagues ; but the 

 marks of sea-action are evident farther from the coast ; for instance, 

 in the valley of Guasco, at a distance of between 30 and 40 

 miles*." That the elevations were gradual, is shov/n by the shells 

 being all littoral, or such as live at very moderate depths ; and by 

 their broken condition, and by their becoming more brittle and 

 having a more ancient appearance the higher they are found, they 

 afford evidence that they had formerly been cast up upon a succession 

 of beaches. The escarpments of the successive terraces, on which 

 shells are strewed, in the sinuosities of the valleys that open to the 

 coast, indicate not only gradual upheavals, but intervals of rest. At 

 Coquimbo there are five such terraces, one above another, in a 

 height of 364 feet. 



Although they relate to an earlier period of geological time than 

 that now under consideration, I shall pass to some other parts of 

 the work of Mr. Darwin ; and I do so the more willingly, because 

 the phsenomena he describes, in the account he gives of his exami- 

 nation of that part of the Cordillera of Chile, are connected with great 

 internal movements, analogous to those which have elevated the land 

 near the coast, on both sides of the South American continent, in 

 comparatively modern periods. 



That part of the Cordillera which forms the eastern boundary of 

 Chile is not more than about 60 miles wide ; and, if we except the 

 volcanic peaks, which occur only at distant intervals, the highest 

 mountains do not much exceed 14,000 feet above the sea. The plain 

 of St. Jago, at their base on their western side, is 2300 feet ; that of 

 the Pampas, on the eastern side, 3300 feet in height. " Although I 

 crossed the Cordillera," says Mr. Darwin, " only once by the Portillo 

 or Peuquenes Pass, and only once by that of the Cumbre or Uspal- 

 lata, riding slowly and halting occasionally to ascend the mountains, 

 there are many circumstances favourable to obtaining a more faithful 

 sketch of their structure, than would at first be thought possible 

 * Pages 53-57. 



