The direction of the most conspicuous mountains is, however, a little different from this ; the principal chain first consti tutes the Pyrenees,and divides Spain from France ; then passes through Vivarais and Auvergne, to join the Alps, and through the south of Germany to Dalmatia, Alba nia and Macedonia ; it is found again be yond the Euxine, under the names of Taurus, Caucasus, and Imaus, and goes on to Tartary and to Kamschatka. The pe ninsula of India is divided from north to south by the mountains of Gate, extend ing from the extremity of Caucasus to Cape Comorin. In Africa, Mount Atlas stretches from Fez to Egypt, and the mountains of the Moon run nearly in the same direction : there is also a considera ble elevation between the Nile and the Red Sea. In the new world, the neigh bourhood of the western coast is, in ge neral, the most elevated; in North Ame rica, the Blue Mountains, or Stony Moun tains, are the most conisderable ; and the mountains of Mexico join the Andes or Cordeliers, which are continued along the whole of the west e..„ b up y America.:lations, and There are several points, in mispheres, from which we may three rivers separating to run to different such are, Swisserland, Bjelosero, Tibet,Nigritia or Guinea, and Quito. •'„, The highest mountains are, Chimboracao, and some others of the Cordeliers in Pe ru, or perhaps Descabesado, in Chili, Mont Blanc, and the Peak of Teneriffe. Chimboracao is about seven thousand yards, or nearly four miles, above the level of the sea; Mont Blanc, five thou sand, or nearly three miles ; the Peak of Teneriffe, about four thousand, or two miles and a quarter ; Ophir, in Sumatra, is said to be five or six hundred feet high er. It has, however, been asserted, that some of the snowy mountains to the north of Bengal are higher than any of those of South America. The plains of Quito, in Peru, are so.much elevated, that the ba rometer stands at the height of fifteen inches only, and the air is reduced to half its usual density. But none of these heights is equal to a thousandth part of the earth's semi-diameter, and the great est of them might be represented, on a six-inch globe, by a single additional thickness of the paper with which it is covered. Mount Sinai, in Japan, Mount Caucasus, Etna, the Southern Pyrenees, St. George among the Azores, Mount Adam, in Ceylon, Atlas, Olympus, and Taurus, are also high mountains ; and there are some very considerable eleva tions in the island of Owyhee. Ben Ne vis, in Scotland, is the loftiest of the Bri tish hills, but its height is considerably less than a mile.
The most elevated mountains, except. ing the summit of volcanos, consist of rocks, more or less mixed, without regu lar order, and commonly of granite or porphyry. These are called primary mountains ; they run generally from east to west in the old world, and from north to south in the new ; and many of them are observed to be of easier ascent on the east than the west side. The secondary
mountains accompany them in the same direction ; they consist of strata, mostly calcareous and argillaceous, that is, of the nature of lime-stone and clay, with a few animal and vegetable remains, in an ob. scure form, together with salt, coals, and sulphur. The tertiary mountains are still smaller; and in these, animal and vege table remains are very abundant; they consist chiefly of lime-stone, ala baster, building-stone, mill-stone, and rnixeu ining in all possible directions, and occupying vacui ties, which appearto be of somewhat later date than the original formation of the mountains. The volcanic mountains in terrupt those of every other description, without any regularity, as if (heir origin were totally independent of all the rest.
The internal constitution of the earth is little known from actual observation, for the depths to which we have penetrat ed are comparatively very inconsiderable, the deepest mine scarcely descending half a mile perpendicularly. It appears, that the strata are more commonly in a direction nearly horizontal than in any other ; and their thickness is usually al most equable for some little distance; hut they are not disposed in the order of their specific gravity, and the opinion of their followipg each other in a similar series, throughout the greater part of the globe, appears to rest on very slightfoundations.
From observations on the attraction of the mountain Schehallien, Dr. Maskelyne inferred the actual mean density of the earth to be to that of water as four and a half to one, judging from the probable density of the internal substance of the mountain, which he supposed to'be asolid rock. Mr. Cavendish has concluded- more directly, from experiments on a mass of lead, that the mean density of the earth is to that of water as five and a half to one. Mr. Cavendish's experiments, which were p6formed with the apparatus invented and procured by the late Mr. Michell, ap pear to have been conducted with all pos sible accuracy, and must undoubtedly be preferred to conclusions drawn from the attraction of a mountain, of which the in ternal parts are perfectly unknown to us, except by conjectures founded on its ex ternal appearance. Supposing both series of experiments and calculations free from error, :t will only follow, that the internal parts of Schehallien are denser, and per haps more metallic, than was before ima gined. The density assigned by Mr. Cavendish is not at all greater than might be conjectured from observations on the vibration of pendulums : Newton had long ago advanced it as a probable supposition, that the mean density of the earth might be about five or six times as great as that of water, any' the perfect agreement of the result of many m *lent experiments with this conjecture affords us a new proof, in addition to many others, of the accuracy and penetration of that illustrious philoso pher. See GLOBES.