equal mass of water, is known more nearly than that of most bodies on its surface. This is rather more than five times (5.66) that of water, or half that of pure silver, and a third less than iron; gold is more than three times, and platinum and some other metals almost four times heavier, so that only a small part of the interior can be filled with matter nearly equal to these whole globe is only twice that of the exterior crust, and as the pressure in the interior must be enormous, condensing any substance exposed to it to a vast amount, it has not unreasonably been imagined that the interior is filled with substances lighter than those forming the external crust. But the heat which hot springs, volcanoes, and experiments in mines, show to exist in the interior, must act as an antagonist power to the compression, and modify its results to a great extent. Hence much uncertainty prevails in regard to the interior structure of the globe. Our planet is not an exact sphere, but only a near approach to this figure. It is flattened or pressed in at the poles, and bulges out in the region through which the equator passes. In consequence of this, the surface of the sea under this line is about thirteen miles higher or more distant from the centre than at the poles. It is supported at this height by the rotation of the earth on its axis, which has a ten-metals in density. The average of the dency to throw any loose body off from the surface, in the same manner as a stone whirled round in a sling. Were the earth, therefore, to stand still, the waters would instantly commence flowing toward the poles, and deluge the highest land around them. Such a catastrophe is prevented by the permanent regular motion impressed on the globe, and its stability, with the proper distribution of land and water on its surface, secured by the form which it now possesses. This is, notwithstanding its various inequalities, very nearly that figure which all the particles composing it, if allowed to move freely among each other, would assume. Were the earth fluid, it would acquire this shape exactly, and its near approach to it, is often taken as a proof that it was formerly in that condition. This, however, is not necessarily true, since it may be shown that the causes now acting on the surface-the wearing down of the highest mountains and hardest rocks, and the transportation of their materials from place to place by rivers and tides-would, in the course of time, produce the same effect. It is also but reasonable to suppose, that if the earth was created at first of solid materials, these would be disposed in that form which was most consistent with the continuance and order of the system. Nothing we perceive in nature at all supports the notion, now so prevalent, that the glorious and perfect arrangement of the universe is the mere necessary development of physical laws. The all-regulating hand of the Creator, seems to have been always present in every corner of his works. To weigh the earth in a balance, might appear to surpass not merely the ability, but the presumption of men. Yet they have not only attempted, but performed this with surprising accuracy, and its specific gravity, or weight compared to that of an That portion of the crust which is accessible to man, is not very extensive; the deepest mine, added to the highest mountain, not exceeding six English miles, or about a thirteen hundredth part of the earth's diameter. Nor is even this visible in any one place, the deepest natural or artificial sections being much less. This crust is composed of rocks, these of simple mineral, and these again of the elementary substances of the chymists. Of the latter, fifty-five or fifty-seven are enumerated, but some of them are very rare, and only found in a few unimportant bodies. The great mass of the earth's crust, consists of scarcely a dozen elements, either alone, or more commonly united with each other in various proportions. These are named simple minerals, which have not only a definite chymical composition, but also a peculiar regular structure, and a tendency to assume certain external forms. This is named crystallization, and is well illustrated by salt or sugar, when slowly deposited from a solution. With rare exceptions, each distinct chymical compound has its own form of crystals, and also peculiar colors and other physical properties, by which they are distinguished from all others. The number of these minerals now known is about four FORM AND STRUCTURE OF THE EARTH. 275 hundred, but not a seventh of these are of | yellow varieties for gold. Common grancommon occurrence, and the vast proportion of rocks are composed of less than a dozen. ite consists of these three minerals, in various proportions, and is of a white or red color. Besides them, however, a fourth mineral, of a dark green or black color, occurs in it. This is named hornblende, and much resembles another green mineral, named augite. Geologists use the word rock in a more extended sense than in common language. All the great extended masses composing the crust of the earth are rocks, and even beds of sand or clay receive the same name. Rocks are either simple, consist-most the whole rocks on the earth consist, ing of one mineral, or compound, composed of two or more. Quartz, or the silica of the chymists, occurs in a great variety of forms. It is itself a compound substance, formed of oxygen, the vital air we breathe, and of silicon, formerly believed to be a metal, but now placed by chymists in a different class. Its compound, silica, is the most abundant substance on the globe, forming more than half of that part of it with which we are acquainted. The common white "chuckie-stones" of children, is one of its most characteristic varieties; the gun-flints of the sportsmen were fashioned from another, the dark color being caused by some extraneous mixture; and the fine pure rock crystal, the Cairngorm stones, the amethyst, cornelian, and jasper, are all other varieties of this mineral, in more or less purity. It has many colors, yellow, brown, red, green, blue, and black, but is most commonly white or gray. It also appears when crystallized in several forms, but very frequently in six-sided prisms, ending in a pyramid with the same number of planes. Besides the quartz forming the sandstone, two and sometimes three other minerals are found in it. The quartz is usually of a white color and glassy aspect, but along with it is another mineral of a duller white or red color, and less hard, named felspar. Of this there are several varieties, differing in chymical composition. Besides silica and alumina, which form clay when decomposed, the common felspar contains potash; a second variety contains soda, and a third also lime. Granite, besides these two minerals, contains mica, well known from dividing into thin, transparent, elastic plates, of a bright silvery color. It has so much the appearance of a metal, that ignorant persons often mistake it for silver, and the Of these five minerals, now named, al and there are few which do not contain one or other of them. The only other substances of much importance are lime, the carbonate of which forms the common limestone, and marble; and iron, a small proportion of which is found in almost every rock, while its ores, from which the metal can be prepared, are very abundant. From these few minerals, with some others of rarer occurrence, a great variety of rocks are formed, some geologists enumerating from two to three hundred species. The three kingdoms of nature, the animal, vegetable, and mineral, though widely distinguished, are yet closely connected. The lifeless inorganic mineral could exist without the plant or animal, but these are not equally independent. Not only does the mineral kingdom form the rocks and soil on which they live and vegetate, but from it also they draw their food and nourishment. The plant converts the inorganic elements into a state adapted for the support of animals, which seem incapable of performing this office for themselves, and, on their dissolution, their bodies are again restored to the earth whence they have literally been taken. There is thus a continual wonderful circulation of material elements, from the mineral, through the plant and animal, back to the mineral again. But the plants deriving their support from the soil, it is necessary that they should find in it the various elements on which they exist. Were any of these wanting, they would either perish, or become sickly and unfit for the nourishment of animals. Hence the great importance of the compound nature of rocks, from whose decomposition the soil is formed, as plants are thus furnished with those substances which they require. The two rocks just mentioned are a good illustration of this. The sim ple rock, the sandstone, consisting of silica alone, decomposes into a very barren and unfruitful soil. In granite, the silica also prevails, but mixed with six or eight other substances, and the soil, though far from fertile, is much more so than that over pure sandstone; while, hills, though high, are covered with fine grass, and in the south of Europe, with forests of oaks and chestnuts. But still greater variety of rocks, and the more compound soil they produce, are more favorable to vegetation. of origin deduced from their internal structure? Sand or mud, deposited from water, is seen to form beds or layers of greater or less extent, and these should be seen in the sandstone rocks, if this is the manner in which they have been produced. And such, every one who has looked into a sandstone quarry, must have observed to be the case. The sandstone is, on this account, said to be stratified, or to form strata, a word derived from a Latin verb signifying to strew or spread out, as the materials of the sandstone beds are supThe sandstone and granite also furnish posed to have been at the bottom of the good illustrations of some other distinc- sea, or in some other large body of water. tions of great importance in geology. The The granite having a different origin, does name of the former implies that it consists not exhibit this peculiarity. It appears in of sand, that is, of grains of a round ir- large irregular masses, divided in various regular form. These grains are of vari- ways, but not into regular beds; and most ous sizes, from a pin head, or even less, of the rocks, whose structure is like its to that of a pea or marble. When larger, crystalline, are also massive and unstratithe rock is named a conglomerate, though fied. Many of them, indeed, appear like its structure of broken fragments is still a mass of molten metal poured out through the same. In granite, the distinct miner- an opening on the surface of the ground. als are mixed together in apparently an ir-Some of these details may seem uninterregular manner, but each portion has a esting to our readers, but they constitute definite form, is bounded by straight lines the first principles of all geological science, or smooth planes, and the rock, when and even in themselves are not barren of newly broken, shows numerous shining remarkable results. It was long a favorsurfaces which reflect the light, instead of ite endeavor of philosophers, misled by a rough uneven fracture like the sandstone. the desire of simplicity, to endeavor to The granite is thus named a crystalline explain all the phenomena of the earth by rock, whereas the sandstone is said to be one agent, by fire or by water. But even uncrystalline, and this difference is be- these two rocks, found in great abundance lieved to arise from a difference in their in most quarters of the earth, show that mode of origin. Sand-broken irregular neither of these theories is alone sufficient, grains-is produced by water from the de- and that facts require both to be combined. struction of previous rocks, as on the It will also be found that both agents, and banks of rivers or the seashore. Where the rocks which they produce, serve imwe see heaps of sand strewed on the sur-portant purposes in the economy of creaface, we immediately conclude that water, and water in motion, has in some former time been there. Grains or crystals, like those of the granite, do not arise in this way. They are only seen to form where the substance composing them has been dissolved, either in a fluid or by heat, so that its particles can unite in a regular manner. Hence it is supposed that granite, and the rocks which resemble it in structure, have been formed in one of these ways, and probably in the latter, or from a state of igneous fluidity. But, it may be asked, do the external forms of these rocks agree with this mode tion, and produce, by their union and opposition, a system that is far more perfect and beneficial than would have resulted from either of them alone. Even looking at these rocks, in the low and limited light of materials for human dwellings and other edifices, it will be found that each possesses peculiar properties and advantages, which could not have been combined, and one class of which, therefore, must have been sacrificed, had fire or water alone prevailed in the formation of the earth. TAKE care of your business, and your business will take care of you. THE NARWAL. THE NARWAL. MONG the ceta- of the most remarkable. Its general form resembles that of the porpoise; it has however no teeth, properly so called, but two tusks, or spears, implanted in the intermaxillary bone, but of which the right remains usually rudimentary and concealed during life. The left tusk, on the contrary, attains to from five to seven or eight and sometimes ten feet in length, and projects from the snout in a right line with the body, tapering gradually to a point, with a spiral twist (rope-like) throughout its whole extent. In structure and growth, this tusk resembles that of the elephant, being hollow at its base, or root, and solid at its extremity. 277 |lous land-unicorn, and therefore they were valued as an inestimable curiosity, and sold excessively dear, till the Greenland fishery was set on foot, when they found them in the northern parts of Davis's straits in greater plenty than anywhere; yet for sometime they carried on the cheat." Captain Scoresby found the remains of cuttle-fish in the stomachs of several which were opened by him, and similar remains were also found in the stomach of one driven ashore near Boston, Lincolnshire, England. In general form, the narwal resembles the porpoise, or grampus, but the head is small and blunt; the mouth is small, and not capable of much extension. The under-lip is wedge-shaped. The eyes are placed in a line with the opening of the mouth, at the distance of thirteen or fourteen inches from the snout, and of small size, being about an inch in diameter. The spiracle, or blow-hole, is a single orifice of a semicircular form, on the top of the head, directly over the eyes. The The tusk or spear of the narwal con- fins, or flippers, are about fourteen or fifstitutes a powerful weapon, which it is teen inches long, and from six to eight reported to use with terrible effect. It is broad, their situation on the sides of the however its only weapon, for it has neith- animal being at one fifth of its length from er the formidable teeth of the grampus nor the snout. The breadth of the tail is from of the cachalot. Crantz thus describes fifteen to twenty inches. There is no the narwal: "This species is commonly dorsal-fin, but a sharp ridge runs down the twenty feet long, and has a smooth black centre of the back, the edge of which is skin, sharp head, and little mouth. A generally found to be rough and worn, as round double-twisted horn runs straight if by rubbing against the ice. Crantz out from the left side of the upper lip. It describes the narwal as being black; it is commonly ten feet long, as thick as is only in young specimens that this color one's arm, hollow inside, and composed can be said to prevail: at an early age the of a white solid substance. It is proba- narwal is blackish-gray on the back, with ble he uses this horn to get at the sea- numerous darker spots and markings rungrass, which is his proper food, and also ning into each other, forming a general to bore a hole in the ice with it when he dusky-black surface. The sides are alwants fresh air; possibly also as a weap-most white, with dusky and more open on against his enemies. Another little horn, a span long, lies concealed in the right side of his nose, which probably is reserved for a fresh supply, if some accident should deprive him of the long one; and they say that as a ship was once sailing at sea it felt a violent shock, as if it had struck upon a rock, and afterward one of these horns was found fastened in it. Formerly these horns, or tusks, were looked upon to be the horns of the fabu markings; the under surface is white. In adult specimens, the ground-color of the back is yellowish-white, with markings varying from dark gray to dusky-black, and of a roundish or oval figure, with interspaces of white or yellowish-white between them. The skin resembles that of the common Greenland whale (balæna mysticetus), but is thinner. The female narwal produces a single young one at a birth, which she nourishes with milk for |