Granite, Gneiss, And All The So-Styled Primitive Neptunian Mountains, May Possibly Owe Their Origin To Volcanic Forces, As Well

As the trachytes; but to forces of which the action resembles less the still-burning volcanoes of our days, ejecting

Lava, which at the moment of its eruption comes immediately into contact with the atmospheric air; but it is not here my purpose to discuss this great theoretic question.

After having examined the general structure of South America according to considerations of comparative geology, I shall proceed to notice separately the different systems of mountains and plains, the mutual connection of which has so powerful an influence on the state of industry and commerce in the nations of the New Continent. I shall give only a general view of the systems situated beyond the limits of the region which forms the special object of this memoir. Geology being essentially founded on the study of the relations of juxtaposition and place, I could not treat of the littoral chain and the chain of the Parime separately, without touching on the other systems south and west of Venezuela.

A. SYSTEMS OF MOUNTAINS.

A.1. CORDILLERAS OF THE ANDES.

This is the most continuous, the longest, the most uniform in its direction from south to north and north-north-west, of any chain of the globe. It approaches the north and south poles at unequal distances of from 22 to 33 degrees. Its development is from 2800 to 3000 leagues (20 to a degree), a length equal to the distance from Cape Finisterre in Galicia to the north-east cape (Tschuktschoi-Noss) of Asia. Somewhat less than one half of this chain belongs to South America, and runs along its western shores. North of the isthmus of Cupica and of Panama, after an immense lowering, it assumes the appearance of a nearly central ridge, forming a rocky dyke that joins the great continent of North America to the southern continent. The low lands on the east of the Andes of Guatimala and New Spain appear to have been overwhelmed by the ocean and now form the bottom of the Caribbean Sea. As the continent beyond the parallel of Florida again widens towards the east, the Cordilleras of Durango and New Mexico, as well as the Rocky Mountains, merely a continuation of those Cordilleras, appear to be thrown still further westward, that is, towards the coast of the Pacific Ocean; but they still remain eight or ten times more remote from it than in the southern hemisphere. We may consider as the two extremities of the Andes, the rock or granitic island of Diego Ramirez, south of Cape Horn, and the mountains lying at the mouth of Mackenzie River (latitude 69 degrees, longitude 130 1/2 degrees), more than twelve degrees west of the greenstone mountains, known by the name of the Copper Mountains, visited by Captain Franklin. The colossal peak of Saint Elias and that of Mount Fairweather, in New Norfolk, do not, properly speaking, belong to the northern prolongation of the Cordilleras of the Andes, but to a parallel chain (the maritime Alps of the north-west coast), stretching towards the peninsula of California, and connected by transversal ridges with a mountainous land, between 45 and 53 degrees of latitude, with the Andes of New Mexico (Rocky Mountains). In South America the mean breadth of the Cordillera of the Andes is from 18 to 22 leagues.* (* The breadth of this immense chain is a phenomenon well worthy of attention.

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