or truncated by some accidental cause. Their towering summits seem to menace the neighbouring country. The basaltic mountains also present an appearance not less striking when they are not covered and concealed by other soil. Their sides display to the view close ranges of immense pillars or causeways, which seem to be the productions of giants.

Single detached elevations of great height are rare, but mountains are generally found in lofty bands, consisting either of one central chain, with branches running off at right angles, or of several chains or ridges running parallel to each cther; and, in both cases, often accompanied by subordinate chains of a smaller elevation. A group of mountains is a collection of several chains; a system of mountains is a collection of groups.

The most general view of mountain systems shows us a vast mountainous zone almost completely surrounding the basin of the great Pacific Ocean; rising from the southern extremity of South America, the lofty rampart of the Andes extends along the western coast of the American continent, at no great distance from the sea, through a length of 9,000 miles, and, sweeping round in a semicircle through Asia, a continuation of the same great barrier, under the various names of the Altai, Himalaya, and Taurus, crowns the summit of the declivity down which the great Asiatic rivers descend into the ocean. The Caucasian, the Carpathian, and the Alpine chains, are a prolongation through Europe of the colossal girdle.

The following is the height of the loftiest peaks in the different quarte's of the globe.

Feet.

South America, (Andes Nevado de Sorato,) 25,400

In the benevolent purposes of Providence, these great elevations of the earth's surface are made subservient to the well-being of the animal creation. Rising into regions of perpetual ice, they serve in hot climates to cool the burning air, and to fan the panting inhabitants with refreshing breezes; they are the reservoirs of rivers, supplying their shrinking streams in the dry seasons of the lower countries with copious torrents from the melting snows; they are the storehouses of the richest minerals; they increase the surface of the earth, and give diversity and richness to its vegetable products; and how often have they not served to stay the march of the conqueror, and to shelter in their fastnesses the last champions of freedom!

ISLANDS. - The Eastern and Western continents are, strictly speaking, two great islands, washed on all sides by the ocean; but, setting these aside under the name of continents, we generally restrict the application of the term islands to smaller masses of land lying in the midst of seas or lakes.

Islands are sometimes detached, but oftener collected into groups or archipelagos; in some cases they are little more than low sand-banks, ledges of rocks, or coral reefs, and in others, rising to a considerable elevation above the surface of the water, and, spreading to a con

siderable extent, they present in miniature all the features of the continents, hills, valleys, plain lakes, streams, &c.

They are often the summits of submarine muntainous chains, and as such are intimately connecte with each other, and with the neighbouring contine; in general, they are considered as appendages to the earest main land. Many of them are evidently the vraduction of submarine volcanoes, which heave them un from the bosom of the waters, and fertilize their surface by the matter ejected from their bowels.

The largest islands of the globe are Borneo, New Guinea or Papua, Greenland, Sumatra, Madagascar, Niphon, Cuba, Great Britain, &c.

CAVERNS.-Caves or grottos are cavities of greater or less extent, which have been formed by different causes in the crust of the earth. They are either open to day, or are more or less completely concealed in the interior of the earth.

There are many different modes in which these wonders of nature are formed. Those in limestone and gypsum appear to have been produced by the dissolving power of water, which has thus hollowed out the rock, and carried off the dissolved materials. Those in lava and trachyte are produced by the expansive power of gases or vapors, operating upon the rocky mass in a state of fusion, or softened by heat. Others are the effect of rents in the crust of the earth, occasioned by earthquakes.

Stalactites and stalagmites are formed by the filtration of water containing calcareous matter through the pores or fissures in the roofs of limestone caverns.

When the water deposits its lime, as it drops from the roof of the cavern, it forms long rods of stone, hanging down like icicles, which are called stalactites; but when the water falls to the floor, or trickles down the sides of the cavern, the calcareous crust formed by its evaporation is called a stalagmite. The masses thus produced, whether pendent from the roofs or rising from the floor, often assume shapes resembling objects of nature or art, and frequently give the cavern a highly brilliant appearance.

CAVES OF AMERICA. The cave of Guacharo, near Caripe, in Venezuela, is so called from the vast flocks of nocturnal birds of that name which frequent it, and which are killed in great numbers for their fat. It is 85 feet broad and 77 high at its opening, and preserves these dimensions for the distance of about a quarter of a mile. A river issues from it, but it has never been explored.

Near the Duida Mountain, in the valley of the Orinoco, there is the vast cave of Ataruipe, remarkable as containing the skeletons of an extinct tribe of natives, and urns filled with bones, which have been prepared by drying in the sun, or by being besmeared with resins or some coloring matter.

Nickojack Cave, in the northwestern part of Georgia, which is 50 feet high by 100 wide, and is traversed by a stream of considerable size, has been explored to the distance of three miles.

Wyer's Cave, in Virginia, contains a series of large halls extending for the distance of half a mile, and adorned with glittering stalactites.

Mammoth Cave, in Edmonson county, Kentucky, is

one of the largest that has been discovered; it extends ten or twelve miles, containing a great number of long passages and vast halls; one of these, called the Temple, is said to be eight acres in extent, with a roof lʊ0 feet high, unsupported by a single pillar; from this numerous avenues lead to several other apartments little inferior in size. A large hotel has been built in this wonderful cave, and sixty persons sometimes may be seen dining there.*

CAVES IN EUROPE. - One of the most remarkable of these is Fingal's Cave, in the island of Staffa. Its entrance, 66 feet high by 42 wide, leads into a natural hall about 200 feet in length, which is bounded on all sides by regular columns of basalt. It was not discovered till 1772.

The Peak Cavern, near Castleton, Derbyshire, England, is a huge gulf, 42 feet high and 120 feet long, at the foot of perpendicular cliffs of amazing height. Thence the visiter is conducted through a succession of dark, cavernous apartments, and ferried along a subterraneous river, above which the rocks are so close, that he is obliged to lie flat on his face. This terminates at the distance of about 2,000 feet.

Poole's Hole, near Buxton, is chiefly remarkable for the large masses of stalactite and other petrifactions with which it is filled. It derives its name from its having been the retreat of a famous robber of the sixteenth century.

Bauman's Cave, in the Hartz Mountains, consists of a series of rooms, six in number, having a total length

* For a fu description of this and other caves, see "Wonders of Geology.