duced by a division of the mountain. Such instances frequently occur in the Alps, the Pyrenees, and other chains. 237. The valleys of lowland regions are not usually definite in their form, and gradually descend into the plains around them but those of elevated regions are usually enclosed by mountains. ; 238. They are generally long and narrow; some, however, are round like the basin of a lake; as in those of Bohemia and Cashmere. Such valleys often contain lakes, and a set of rivers which have no other outlet. This is the fact with the Lake of Titicaca, in South America; the Sea of Aral in Asia; and many small lakes in other countries. 239. Passes or defiles are narrow valleys which pass through chains of mountains, and are often the scenes of battles; as the celebrated pass of Issus, and the straits of Thermopyla. 240. These openings are also termed the gates of the country. Such are the gates of the Caucasus, and the gates of the Caspian, which form the only passages to Asia, between the Black and Caspian Seas. In the United States, they are usually termed gaps or notches. In many instances they are mere chasms of great depth, with perpendicular sides; as among the White Mountains. The principal pass in the White Mountains, is "The Notch," which seems to cleave the group to its base. It extends for two miles, between lofty walls of rocks, in one part only 22 feet distant from each other; and presents every where a striking assemblage of rocky ruins. 241. The Andes abound in chasms of a similar kind, called quebradas, some of which are nearly a mile in depth. They render travelling dangerous, and are crossed only by bridges of ropes. 242. Sometimes a defile forms the passage of a river, and presents a scene of striking grandeur; as in the passage of the Potomac through the Blue Ridge, and the Missouri through the Rocky Mountains. Such also is the passage of the Susquehannah through the water-gap of the Blue Ridge; and of the Hudson River through the high precipitous mountains, called the Palisadoes. The gates of the Rocky Mountains, which form the passage for the Missouri, present a sublime spectacle. The river is only 450 feet broad, and runs for nearly six miles between overhanging precipices, 1200 feet in height. 243. It is the opinion of the most celebrated naturalists, that the chasms and valleys of the earth, could not have been produced by any cause now in operation. Such immense and extensive changes can only be ascribed to a universal deluge.* 244. The chasm which forms the channel of a river, is sometimes covered with a portion of the rock, which seems not to * See Brogniart-Buckland, &c. have been removed by the convulsions that have produced it, and forms a natural bridge. 245. The most celebrated curiosity of this kind, is the bridge which passes over Cedar Creek, in Rockbridge, Virginia. It consists of a lofty arch of rock, covered with earth and trees, passing across the chasm, at the height of 210 feet above the water. [31] The bridge is about 65 feet wide, and 40 in thickness. "The view from below is as delightful, as that from above is painful. The arch seems to spring almost to the sky; and no scene of nature can produce higher emotions of the sublime."* In Scott County, Virginia, there is a similar bridge, 1000 feet long, and 300 high; and in Berkshire County, Massachusetts, is one 60 feet high. 246. At Icononzo, in South America, on the route from Santa Fe de Bogota to Popayan, there are two remarkable bridges of this kind, 300 feet high. They cross an immense chasm, forming the bed of a torrent which could scarcely have been passed in any other way. Two others occur in Mexico. 247. An appearance not unlike that of a natural bridge, is presented by mountains which are pierced by a cavity passing through them. Mt. Torghat in Norway is thus pierced, by a cavity 180 feet in height, and 3000 in length. A rock near New Zealand, and the Doreholm, in the isles of Scotland, are pierced in the same manner by an arch through which the sea passes. 248. Mountains assume a great variety of forms, according to the rocks of which they are composed. Sometimes they rise like a dome or a bell, and sometimes shoot up in a form which gives them the name of needles. Chains are frequently diversified with numerous pointed peaks, which have led the Spaniards to give them the name of sierra, or saw. 249. Volcanic peaks are generally distinguished by their regular conical form, produced by the materials thrown out from the top; as in Etna, and the Peak of Teneriffe. 250. Mountains of granite, of which the Alps and Norwegian Mountains furnish striking examples, are usually broken into rugged, lofty peaks, abounding with steep cliffs. The valleys are, in general, deep and narrow, and often bounded by precipices. The Table Mountains, one in South Carolina, and one at the Cape of Good Hope, are striking examples of precipices of granite. The latter is 3000 feet high. 251. Mountains composed of stratified rocks, such as gneiss, mica slate, and clay slate, are less rugged. In passing through the transition to the secondary class, they become smooth and * Jefferson's Notes. round-backed; and in the secondary regions, are reduced to gentle swells and valleys, which appear like the waves of the sea. 252. Limestone of the transition and secondary formations, is marked by deep valleys, and numerous chasms and caves, and often presents rough cliffs and precipices. The upper or flatz limestone usually forms extensive tracts of flat country. Kentucky and Tennessee furnish examples of these appearances. The chasms are so numerous in some parts, that they often absorb the waters of springs and streams, and produce a drought. 253. Mountains of sandstone are seldom of any great height; and as this rock easily decays, they present a great variety of forms. In the uppermost sandstone, the valleys are deep and romantic; the hills conical, steep, and abounding in cliffs; and it often presents grand colossal pillars and masses, which form the most striking rocky scenes. In some instances, they appear at a little distance like a city in ruins; as in 132 several parts of Africa, and on the banks of the River Volga; and they have sometimes been described as such. The Castle Rock, observed by Major Long, near the Rocky Mountains, has a similar appearance. 254. Mountains of trap rocks are composed of columns of five or six sides, divided into joints, which are closely united to each other, and appear like a solid honeycomb. They present high precipices, which often have the regularity of walls constructed by art. A mass of fragments generally lies at the base; and the whole appears like the ruins of immense towers or castles. (12.) The Giant's Causeway. 255. Striking examples of this formation are seen in the basaltic rocks, on the northern coast of Ireland, of which the Giant's Causeway is the most celebrated. It consists of three piers of columns, extending several hundred feet into the sea, whose tops present a level pavement of stone. The columns rarely exceed 30 feet in height. More striking appearances are found in other parts of this basaltic range, which extends along the coast 40 miles in length, and 20 in breadth. The two most remarkable points are the promontories of Fairhead and Bengore. They consist of similar ranges of columns, rising 150 feet perpendicularly at Fairhead, and at Bengore 400 feet. 256. The Hebrides, or Western Isles of Scotland, present similar examples of basaltic columns; and those of a less perfect kind are found in the United States, in the Palisadoe Rocks of the Hudson River-at East and West Rock, near New-Haven, in Connecticut-at Mount Holyoke, near Northampton, and other places in the range of mountains extending north from these bluffs. 257. The height of mountains of trap is generally small; but in South America, these rocks cover some of the highest peaks of the Andes. [33] It is remarkable, that Chimborazo and Antisana, are crowded by immense walls of porphyry; a rock allied to trap, rising to the height of 6,000 or 7,000 feet; and basalt, which has never been observed higher than 4,000 feet in Europe, rears its castled precipices on the top of Pichinca, 18,000 feet above the level of the sea. 258. The elevation of mountains produces a great effect on the air. As we rise above the level of the sea, it becomes more rarefied. At any considerable height, the difference is so great, that breathing becomes difficult, and all efforts laborious; and the blood often starts from the eyes and lips. The change is so regular and gradual, that a traveller may determine the height of the spot on which he is, by means of the barometer, an instrument which measures the pressure of the air. The elevation of mountains is usually determined in this manner. 259. At the height of two or three miles, the air becomes so dry, as to produce the most distressing thirst. The traveller finds himself elevated above the region of clouds and storms; and often sees them roll and burst beneath him. 260. The heat also diminishes rapidly in ascending mountains. At the height of two and a half miles above the sea, in latitude 40 degrees, and three miles at the equator, the cold is so intense, that every trace of animal life is extinct. All above is the abode of silence and desolation. At this height, snow and ice continue through the year; and hence the peaks of the Andes, the Alps, and other lofty mountains, are whitened with perpetual snow. 261. The elevation of table lands produces the same effects on the air and climate as in mountains; and the distinctions of latitudes and zones are often lost, over a great extent of country thus elevated. 262. The habitations of men are rarely found in Europe above the height of 6,500 feet; and the highest inhabited spot is the monastery of St. Bernard, 8,000 feet above the sea. But in the Torrid Zone of South America, we find large cities, such as Quito and Santa Fe de Bogota, at this height. Considerable settlements, such as the town of Guanca Velica, are still higher; and the single farm-house of Antisana, is 13,400 feet above the sea. 263. Immediately below the region of perpetual snow, wc find in the plains and valleys of lofty mountains, those vast lakes of ice called glaciers. They are formed by the alternate melting and freezing of the snow, by the change of seasons; and therefore occur chiefly in the Temperate and Frigid Zones. They are found of the greatest extent and magnificence among the Alps. These mountains contain not less than 400 glaciers. They are of various sizes, but frequently extend 16 or 18 miles in length, and the total area of their surface is estimated at 1000 square miles. They are from 100 to 600 feet in depth. 264. The surface of the glaciers is, in some cases, smooth and unbroken, and presents an immense mirror of ice. In others, they are broken with waves, and appear like the sea congealed in the midst of a tempest. In many instances they are crossed by [34] deep chasms, and adorned with pinnacles of ice, rising in various forms, appearing like the spires and turrets of a city of crystal. 265. Glaciers also occur in the highest parts of the Pyrenees; and the coasts and mountains of Norway, Lapland, and Spitzbergen, present scenes of desolation of this kind, whose magnificence is beyond description. 266. Vast masses frequently break off from the snows and glaciers of lofty mountains, and roll into the valleys with a tremendous roar. In Switzerland, houses, and even villages, have been buried by these falling masses of snow and ice, which are there called avalanches. 267. At first view, the rugged mountain ranges of the globe appear like deformities on its surface. But they are found to serve important purposes, by the care of HIM who made them. 268. They collect and condense the clouds and vapours, and thus supply the springs and streams which fertilize the earth. The loftiest are covered with perpetual snows, even in the Torrid Zone; and thus serve to cool and equalize the temperature of these burning regions, while they furnish inexhaustible reservoirs for the supply of water. They also arrest the progress |