Mr. Gabb presented a communication on the “Geology of Lower California,” which was referred to the Publication Committee, and ordered printed as one of the Memoirs of the Academy.
Mr. Gabb also communicated the following translation of part of a letter received by him from Sr. Don Antonio Raimondi, of Lima, Peru, with reference to some geological features of that country:
I have just received a letter from Professor Raimondi, accompanying a very interesting collection of fossils, sent through my lamented friend Mr. Rémond, but which I have not yet received. After remarking that he had not time to write a detailed account of the country to assist me in my determinations of the geological ages, he gives the following condensed but interesting description of the country, which I have considered of sufficient value to warrant its immediate publication. I translate this portion of the letter in full.
“Peru, or at least the great chain of the Cordillera which divides the whole of America into two parts, comprises various smaller chains, often very high, and here consisting of four, nearly parallel. The principal of these are two, one of which is the dividing line between the waters emptying into the Pacific on one side, and the tributaries of the Amazon on the other. This is what is properly called the Cordillera of the Andes, or the Western Cordillera. The other chain is called the Eastern Cordillera, and in some points is as elevated or even surpasses in height the true Cordillera. In the southern part of Peru, for example, it is entirely covered with perpetual snow, and contains very elevated peaks, including, in that part which is prolonged into Bolivia, the two colossi called Sorata, or Illampu and Illimani. The Eastern Cordillera is of the greater geological age, appearing to be entirely composed of micaceous and talcose schists which have been metamorphosed by the elevation of the granites, those which have also introduced into these schists numerous veins of quartz, which in some places are quite rich in gold. This elevated chain has been cut very deeply by numerous rivers, which, taking their origin in the Western Cordillera, traverse these immense formations of schists and 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 been worked in many places.
“The volcanic rocks are strongly developed in Peru, especially in the southern 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 action 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 afterwards it approaches almost insensibly the true Cordilleras; so that, near Arequipa, 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 nevertheless 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 sedimentary rocks belonging 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.”