merged beneath the waters.

In the lower strata of the series it is to be observed, that whole genera and species of animals are found which do not now exist in the known world, but as we rise in the series, we find some genera, and at last some species, identical with those now in existence. Yet even these show great changes to have taken place; for it is common to find the remains of tropical plants and animals beneath the surface of countries in which, on account of the coldness of the climate, they could not now live.

3. Age of Rocks. The stratified rocks having been deposited from water, it is obvious that the lowest in the series must have been first deposited, or in other words are the oldest formations, and that the upper beds are the more recent. No such chronological data are afforded by the unstratified rocks, though their relations to stratified materials afford just inferences respecting their true era. Thus if the latter are wholly below all the strata, we infer that they of course existed before any of the stratified rocks were deposited upon them; but if they form lines penetrating some of the strata, and overlying them, then the latter had assumed their present condition before the melted mass was poured into its actual position. Such lines of crystaline rock running through the stratified rocks, are called veins or dikes, and are of common occurrence. Superposition of strata is, then, the chief indication of the relative age of rocks; but as certain organic fossils have been found to be peculiar to certain formations, it is often easy to identify particular rock-formations by their included organized remains, and when the order of superposition cannot be readily ascertained, the nature of these remains will serve to determine the geological age of the rocks. It is on such a basis that the received geological classification of strata has been established; and geologists usually divide them into three great classes, the primary, the secondary, and the tertiary. 4. Primary Rocks. The primary strata are such as do not include any organic bodies.

They are the lowest in the series of strata, and are found to repose on crystaline unstratified rocks, generally on granite, which, as far as the crust has been penetrated, has the appearance of being the general fundamental rock. The name primitive was originally given to these rocks, because they were supposed to have been deposited before the creation of organized bodies; but this cannot be proved, since the cause which crystalized them, or their fusion, may have occasioned the disappearance of organic remains.

5. Secondary Rocks. The secondary strata are generally less crystaline in structure, and in their lower beds the organic remains are few, being chiefly marine productions; but these increase in number and variety in the upper beds, which end with the chalk formation. The organized bodies are chiefly marine productions, as zoophytes, crustacea, shells, and fishes; reptiles, amphibious animals, and plants, are also found in secondary strata. During the deposition of the secondary strata the land appears to have been gradually rising above the level of the waters which once covered it; and during the same period there are marks of more sudden changes or disturbances of the strata, which appear to have been owing to the forcible irruption of melted rocks from the bowels of the earth.

6. Tertiary Rocks. Above the cretaceous or highest secondary strata, another system of deposits appears, which has received the name of the tertiary strata. These have been in part deposited from fresh water, by which circumstance and by their organic remains they are distinguished from the secondary strata. There are, indeed, some fresh-water animals found in the latter, but these are rare, and the formations that include them, seem to have been made in the estuaries of great rivers. But decided alternations of fresh and salt water deposits are characteristic of the tertiary period. All the fossils of the secondary rocks belong to extinct species, and are distinct from those of the tertiary strata. In the latter, mammalia first appear, and there are a few species identical with those now existing.

7. Diluvial Formation. In many countries vast tracts are covered with a confused mass of water-worn rocks, gravel, and a mixture of other fragmentary substances, which completely

The

bury and hide from sight the more consolidated and regular masses above described. rocks are rounded, their sharp edges having been evidently worn off by friction, and the earthy materials have as evidently been produced by the grinding down of the rocky fragments during the same process. Everything here bears the mark of the action of powerful floods of water, which have swept away and ground up or rounded the fragments of native rock; as this formation is the effect of some great deluge, it is called the diluvial formation. Sometimes the masses which have been moved in this manner from their native beds are of great size, and it is possible to trace the direction of the diluvial current by ascertaining their original situation. By this process it is shown that such a flood has swept over the United States from northwest to southeast, scattering over the surface immense numbers of those lost rocks or travelers, as they are often called by the people, or bowlders or erratic blocks, as the geologists term them, to distinguish them from rocky masses in place, that is, in their native beds.

8. Caverns. Fissures and cavities are sometimes found of great extent, forming vast caverns in the bowels of the earth, which are either empty or filled with water. Instances of these on a great scale occur in the limestone strata of many countries, especially of Carniola and the United States. The cavern of Adelsberg, in Carniola, extends several leagues in its various branches, and contains a subterranean lake and river; the not less remarkable Mammoth cave of Kentucky has been traced several miles, and is also in limestone. Some of these caves are brilliantly ornamented with crystals of every shape and hue; such is Weyer's cave, in Virginia, which consists of numerous large apartments and galleries filled with stalactites, or crystaline masses resembling various natural and artificial objects. The celebrated spar cave, of the Isle of Skye, is in sandstone; there is also one in a slaty rock in the island of Thermiæ, and the great Icelandic cave of Surtshellir is in lava. This last is nearly a mile in length, and appears to have been formed in flowing lava by the disengagement of gaseous matters, as it has all the appearance of being the consequence of an enormous air-bubble, having its roof ornamented with projections of black slag. The celebrated Columnar cave on the isle of Staffa, well known as Fingal's cave, is in trap-rock. 9. Minerals. Minerals are divided into four classes; acidiferous, earthy, inflammable, and metallic.

Of the first class, we may notice limestone, calcareous spar, or carbonate of lime, that is, lime combined with carbonic acid. It is the most abundant of any known mineral substance on the earth. It is one of the principal constituents of rocks. It is also found in its pure state in immense beds or banks; of stratified earth it forms more than half. It is also found combined with clay, and thus constitutes the various marls. It forms vast beds, in the shape of chalk, mingled with large masses of shells.

Carbonate of lime, confusedly crystalized, forms a common species of building stone in some countries. When it possesses a finer grain, it forms marble of no great value. As it becomes harder and more refined, it is better adapted for sculpture, and is then properly called marble. White statuary marble from Carrara, in Italy, is esteemed most valuable, and the purest of any. It must be observed, that some kinds of marble are primary and others secondary. There is a fine species of clouded marble found near Middlebury, Vermont. White marble is found in Stockbridge and Pittsfield, Massachusetts, and Washington, Connecticut, and in many other States. A beautiful species, variegated with green, yellow, and black, is found at Milford, near New Haven, Connecticut. In Pennsylvania, several kinds of marble are found, some of which appear to be of primary formation. On the banks of the Potomac, a fine kind of secondary marble, called Breccia, is obtained. The superb pillars which support the dome of the Representatives' chamber in the capitol at Washington, are of this species. Variegated marble is found at Thomaston, in Maine.

Of the second class, or earthy minerals, quartz may be mentioned as one of the most conspicuous. It is everywhere a common stone, and is frequently denominated white flint. Gravel and sand are composed of this mineral. Sometimes it is found in regular crystals, and is then called rock crystal. When transparent it is esteemed very beautiful; and is used for various ornaments. These crystals, when colored, take the name of the precious stones they resemble, and great deception is sometimes practised in making them pass for real gems.

Of this class of minerals, are also the precious stones, which are almost entirely composed of argil, or pure clay. Among the most valuable of these are the ruby, sapphire, emerald, and topaz. The finest rubies and sapphires are found in India and the island of Ceylon. The most beautiful emeralds are obtained in Peru. The most valuable topazes come from Brazil. Feldspar, also belonging to the second class of minerals, forms the base of a multitude of rocks. The whitish particles observed in granite are feldspar, which constitutes two thirds of its substance. Extensive mountains are in some instances solely composed of it. It sometimes occurs in large masses, beautifully colored, and is used for various ornaments. It is found more frequently in the mountains of Asia than in those of Europe. America affords it in large quantities.

Mica consists of thin scales of a metallic brilliancy. It forms a part of the substance of granite, and may be recognised by its sparkling surface. It is also mixed in other rocks, and constitutes a portion of almost every soil. It sometimes occurs in large plates, and is often called isinglass. It is found in Russia, Siberia, and Soongaria, in large masses, the leaves being sometimes several feet square. In Russia it is used in windows instead of glass.

Asbestos, a celebrated mineral, is chiefly found in the fissures and cavities of primitive rocks, of which it seems to be a decomposition. A detached tuft of this mineral can hardly be imagined, at first sight, not to be a bunch of fine white silk. The ancients made towels, napkins, and head-dresses of it. When these became soiled by use, they were thrown into the fire, and upon being taken out were found to be whiter than if they had been washed. This mineral abounds in Corsica, in the Uralian mountains, and in Greenland. The longest that has been found came from the Pyrenees.

Of the third class of minerals, or inflammable substances, we may first notice sulphur, which is discovered in various situations. It occurs at the mouths of volcanoes, in the form of powder, and sometimes in crystals. It is also found in veins or beds, among sulphate of lime and potter's clay. In this latter situation it is chiefly obtained. Bitumen, in a liquid state, called mineral tar or naphtha, filters through the earth and rocks, and sometimes floats on the water like oil. There are springs of it in Persia. In Parma, in Italy, it is drawn up from wells sunk in the earth for the purpose. It is called asphaltum, and gives name to Lake Asphaltites, or the Dead Sea, in Syria. In Persia, Japan, and other countries, it is used for lamps. In Auvergne, in France, glutinous bitumen covers the earth, and sticks to the feet so as to impede the traveler.

Pit coal is of two kinds, bituminous and anthracite. The former burns most freely, and is most common. Of this kind are the coal mines in England. This coal consists of bitumen united to an earthy base, and is supposed to be formed of vegetable and animal remains, long since deposited in the earth, where, by a process of nature, they have assumed their present form. Anthracite coal consists of carbon accidentally mixed with flint and iron. Of this species are the Lehigh and Schuylkill mines in Pennsylvania.

Carbon exists in nature to a great extent. It enters into the composition of a multitude of

substances, and constitutes the chief ingredient of animal and vegetable matter. Common charcoal consists almost entirely of carbon. The diamond, the most precious of all minerals, is pure carbon. It has been ascertained, by repeated experiments, that the diamond is completely combustible. This, as well as the other fine gems, is found chiefly in South America and in India. It is remarkable, that the precious stones, as well as the precious metals, are confined chiefly to equatorial regions. Amber must be regarded as a mineral, though it seems to be a resinous gum, produced by trees. It is chiefly found in the countries bordering on the southern part of the Baltic Sea. It was formerly taken by the fishermen, in nets, but is now procured by digging in the hills of sand along the coast. The largest piece ever obtained weighed 13 pounds, and is preserved in the royal museum of Berlin.

The fourth class of minerals comprehends the metals. Platina, the heaviest of these, and even more valuable than gold itself, is found in the gold mines of America, and in the Ural mountains. It has been obtained only in small quantities, but has been coined in Russia. Some gold is found in Norway and Sweden. The gold mines of Hungary are more productive; but all the gold mines of Europe are trifling in comparison with those of South America. These mines we shall notice elsewhere, as well as those of Mexico. Gold, in considerable quantities, is found in the Southern States. The islands of Borneo, of Celebes, and of Sumatra, situated under the equator, contain very rich mines of this metal. Nearly all the rivers of Africa bring down with them particles of it, mixed with the sand. Upon the coast of Guinea, it is said, that one person may pick up several ounces in a day. Silver is found in various forms, but most commonly mixed with arsenic, in the state of ore. There are mines in Siberia, Norway, Saxony, the Hartz Mountains, and other places in Europe; but the amount of silver obtained from them is small. The silver mines of Potosi, once the most prolific in the world, are now exhausted. Peru, and many other parts of South America, abound in silver. Mexico has produced annually more than 20,000,000 of dollars. Mercury is found in small quantities, both in America, and in Europe. This metal requires so little heat for its fusion, that it always remains in a liquid state in our climate. In the arctic regions it becomes solid; it is then almost as malleable as tin.

Lead is generally found mineralized by sulphur, forming an ore called galena, which is almost always mixed with iron, with antimony, and especially with silver. Lead is not found in abundance anywhere in the north of Europe or Asia. It exists in great quantities in Germany, France, and England. The lead mines of Missouri, Illinois, Iowa, and Wisconsin, are elsewhere described. Copper is an abundant mineral, and is found in all parts of the world. Tin abounds in Cornwall, in England. It is also found in Saxony, but scarcely ever in other parts of Europe. America and Africa produce little of it. It is found in Hindoostan, Malacca, and the islands of Sumatra and Japan. Iron is extensively distributed throughout the earth. mountains of Norway and Sweden contain immense quantities of it. In the southern part of Sweden and in Missouri are mountains composed entirely of iron ore. The north of Asia abounds in iron. Southern Africa, all parts of the United States, and Canada, are also provided with ample stores of this useful metal.

The

1. Diffusion of Vegetation. The geographical distribution of vegetable forms is chiefly affected by climate, including under this head not only temperature and moisture, but degree of light, and density or rarity of the air, and by soil. We find, indeed, traces of vegetation in the depths of the ocean, in dark caverns, in the hot waters of thermal springs, on the loftiest mountains, and even in the bosom of perpetual snow; but these are comparatively rare and feeble, and the full vigor and glory of vegetable life appear only where it is unfolded under favorable influences. In regard to temperature it will be found, that the distribution of heat, rather than its degree, has the greatest influence upon vegetation; the growth of plants which require a long and moderate heat, depends on the average summer temperature; that of those which require a short but great heat, on the temperature of the warmest month, and that of those which are unable to resist a considerable cold, on the temperature of the coldest month. Thus many of the fruits of southern Europe cannot be raised to advantage in some parts of the United States, because the plants are killed by the frosts, although the length and warmth of the summer are sufficient to ripen their fruits. So maize or Indian corn and tobacco are produced in some parts of America whose winters are excessively severe, because the genial heats of a short summer are more favorable to their maturity than the longer and milder summers of Europe. Some plants require much moisture, but also need the strong light and heat of a clear sun, and will not thrive in the cloudy climates, where a serene sky is almost unknown. Sandy or siliceous soils are necessary for some vegetables, and calcareous ingredients are equally essential to others.

2. Number and Distribution of Species. Each plant has generally a determinate climate to which it is best adapted; there are other climates, however, in which it can be raised, though less advantageously, but beyond certain limits it ceases to grow altogether. The whole number of species at present known amounts to 44,000, but it is estimated that the total number of existing species is about 80,000.

The most simply organized plants, such as mosses, lichens, grasses, &c, which form the lowest order of the vegetable creation are the most widely diffused; the more perfect tribes are in general limited to particular regions, and, in some cases, as for example, the cedar of Lebanon, to a particular mountain or district.

3. Vegetation of the Frigid Zones. There are properly no plants which are peculiar to the frigid zone, because the mountains of the torrid zone, embracing every variety of climate between their base and summit, are capable of producing all the vegetables of the temperate and frigid regions. The number of vegetable species in the frigid zone is small; the trees are