Ol' 



GO PROCEEDINGS OF THE CALIFORNIA 



Western Cordillera, traverse these immense formations of schists anil granite 

 through narrow gorges, and unite to form the large affluents of the Amazon. 



" The Western Cordillera or true chain of the Andes is made up in nearly 

 the whole of its length of rocks of a much more recent age. The principal 

 formations are Cretaceous, Jurassic, Lias and Trias. Another group of rocks, 

 probably Carboniferous, form the great basin of Lake Titicaca and a small 

 spot on the heights of Huanta. This Cordillera has been metamorphosed by 

 various eruptive rocks, the principal of which are porphyries and diorites. 

 These have introduced innumerable metalliferous veins, rich in lead, copper and 

 silver, and which have beeu worked in many places. 



" The volcanic rocks are strongly developed in Peru, especially in the south- 

 ern part, and have never been well studied. According to my opinion, they 

 once formed an extensive chain, which, from its being composed of rocks easily 

 disintegrated, has been in great part destroyed by the actiou of water, so that 

 it is separated mostly by isolated hills ; but from all that I have been able to 

 see, it must have formed at one time an uninterrupted chain, as it appears in 

 the central part of Peru, at a little distance from the Pacific Ocean, and after- 

 wards it approaches almost insensibly the true Cordilleras ; so that, near Are- 

 quipa, it is more than twenty leagues from the sea, but in following it to the 

 south it nears the Cordillera, extending to Cruzalia, in the broken country of 

 Moqueque and Tacna. 



" Along the whole length of the coast, at a distance of one or two leagues 

 from the margin of the ocean, rises a small chain of hills formed of granite, 

 syenites and porphyries. This chain is called ' the Hills' (Lomas) and contains 

 in places scattered spots of copper and a very little gold. On the same coast 

 and on the adjacent islands, sedimentary rocks are rare, though they are never- 

 theless found at rare intervals. To the north, sedimentary rocks extend from 

 Tumbes to the south of Payta, at the little cove of Tortugas, where there 

 are many springs of fresh water in a hardened claystone, alternating with 

 calcareous strata, which contain little seams of coal. 



" From Secharra to near Lima there is no sedimentary formation. Near 

 the port of Ancon, five leagues from Lima, in the island of San Lorenzo, near 

 Callao, and in Chorillo, three leagues south of Lima, there are some stratified 

 sandstones with a very few fossils. These formations appear to us to be either 

 Jurassic or Liassic, but the study of the few fossils found will determine better 

 their age. 



" Near Arica, and three leagues to the interior from Iquique, where are the 

 celebrated silver mines of Huantapaya, there have also been noticed sedimen- 

 tary rocks belongiug to the Oolite and Lias. 



" In the elevated regions of the Cordillera are many traces of stone coal 

 which, unlike those in the formation about Lake Titicaca, which I have already 

 said belong to the true Carboniferous, are all of more recent age, belonging to 

 the Jurassic and Liassic, as you will see by specimens from the Springs of 

 Pariatambo." 



