Essay on the Geography of Plants by Alexander von Humboldt

Author:Alexander von Humboldt
Language: eng
Format: epub
Publisher: University of Chicago Press

I have sketched out here broadly the profile of the high mountain range of the Andes. As far as its structure and the nature of its rocks are concerned, I must limit myself to the following.

The equatorial regions contain all the rocks that have been discovered elsewhere on the earth. The only rock formations that I did not observe there are the steatite rocks, called Topaz rock by Mr. Werner, the mixture of small-grained limestone and serpentine found in Asia Minor, oolite, called Rogenstein by the Germans, greywacke, and chalk. But on the surface of the earth, not only are the rocks identical; there is also a harmonious correspondence between the arrangement and the superimposition of these rock masses, which proves that nature acts everywhere according to laws that are as simple as they are universal. In South America, granite constitutes the basis on which the more recent formations lie. It is exposed at the foot of the Andes, on the South Sea coasts, and on the Atlantic Ocean’s coasts, between the mouths of the Orinoco and the Amazon Rivers. It supports the elevated structure of the Andes as well as the secondary formations in the plains. The granite, filled with quartz, containing not much mica but large feldspar crystals, seems older in the Andes than the small-grained granite that is filled with little hexagonal tablets of mica. Peruvian granite resembles granite in the high Alps and Madagascar: both are in large masses, sometimes in regularly inclined and parallel layers, with embedded round, very micaceous masses, and both owe their origin to particular attractions between their components. Red titanium oxide is more abundant there than tourmaline. Steatite (Speckstein), lepidolite, and barium sulfate have not yet been discovered to be an essential part of granite. On this rock, the most ancient on the planet, and sometimes alternating with it, one finds gneiss, or laminated granite. It yields to micaceous schist, and this in turn yields to primitive schist. In these regions garnet is more commonly found in laminated granite than in micaceous schist. It is even found in the beautiful porphyry that, on top of the schist, crowns the peak of the silver-bearing Potosí mountain. The small-grained limestone rock, chloritic schist, and primitive trap rock (a well-blended mixture of feldspar and amphibole) often occur in subordinate layers in laminated granite and in micaceous schist. The latter is as widespread in the Andes as in the high range of the Alps. It often contains layers of graphite, and is a base for serpentine and jade formations. One sees what has probably not yet been observed in Europe, serpentine alternating with syenite. The high ridge of the Andes is covered everywhere with porphyric formations, with basalts, phonolites, and green rocks. These formations, often divided into separate columns, give to the Cordilleras the aspect of grotesque castle ruins that the spectator first sees when coming upon them from afar. Volcanic fire pierces through these porphyric rocks; and it is a difficult problem for the

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