Mountains are supposed by naturalists to have different origins, and to date their commencement from various periods. Those which form a chain, and are covered with snow, are accounted primitive, or antediluvian. They greatly exceed all other mountains in height; in general their elevation is very sudden, and their ascent steep and difficult. They are composed of vast masses of quartz, destitute of shells, and of all organized marine matter; and appear to descend almost perpendicularly into the body of the earth. Of this kind are the Pyrenees, the Alps, the Himmaleh ranges, the Atlas, and the Andes. Another class are of volcanic origin. These are either detached or surrounded with groups of lower hills, the soil of which is heaped up in disorder, and consists of gravel and other loose substances. Among these are Mount Ætna and Vesuvius. A third class of mountains, whether grouped or isolated, are such as are composed of stratified earth or stone, consisting of different substances of various colors. The interior consists of numerous strata, almost horizontally disposed, containing shells, marine productions, and fish bones in great quantities. The strata of mountains which are lower and of more recent date, sometimes appear to rise from the side of primitive mountains which they surround, and of which they form the first step in the ascent. The mountains in Asia are the most elevated and imposing in the world. Of these the Himmaleh chain is the highest; one of its peaks, Dhawalaghiri, reaching the altitude of twenty-eight thousand and ninety-six feet, and several exceeding twenty-four thousand. Africa has some extensive chains of mountains, but the altitudes of only a few have been ascertained. Mont Blanc is the highest summit of Europe, reaching an elevation of fifteen thousand seven hundred and thirty-five feet. The Andes of South America present the most striking and stupendous features; cataracts, volcanoes, and immense chasms of an almost perpendicular descent. Chimborazo, the highest point of the Andes, reaches twenty-one thousand four hundred and sixty-four feet; in many places the peaks rise to upwards of twenty thousand feet, though in others they sink to less than one thousand. In general, all the chains of mountains in the same continent, seem to have a mutual connection more or less apparent; they form a sort of frame-work to the land, and appear in the origin of things to have determined the shape which it was to assume; but this analogy, were we to generalize too much, would lead us into error. There are many chains, which have very little, or, rather, no affinity to each other. Such are the mountains of Scandinavia and of Scotland, mountains as independent as the character of the nations who inhabit them. TABLE OF THE PRINCIPAL ELEVATIONS IN THE UNITED STATES.