se rocks we find depositions of sand, and ay; accumulations of peat, and other substane progress of deposition, and which are inclu› general terms alluvial formations. These fourth class. The fifth class contains the olcanoes, whether the result of fusion or not, hrown out without melting, volcanic mud, &c. sed that all the formations as they are termdifferent kinds of rocks and strata now found will fall under one or another of these claswill be seen hereafter, that this theory is, in s, unsatisfactory, and that there are several s basalt and greenstone, which certainly are is origin, and which do not come within Werc class. as appointed professor of mineralogy, at the nes, in Saxony, 1775, and was undoubtedly highest order of talents. His mind was at imaginative, and richly stored with miscellaedge. He had a great aversion to the meor of writing, and could never be persuaded than a few brief sketches, and which never connected development of his geological hough the natural modesty of his disposition e, approaching even timidity, yet he indulged old and sweeping generalization, and he inpupils, some of which became writers of great ith the most implicit faith in his doctrines. Imiration," says Mr. Lyell," of his genius, and of gratitude and friendship which they all felt e not undeserved; but the supreme authority urped over his contemporaries, was probably prejudicial to the progress of science." onic, or Huttonian Theory owes its origin to of Edinburgh. It was published in 1788, but pre recently illustrated and defended in a reby Professor Playfair, also of Edinburgh. already stated that the Plutonians attributed enomena to fire, which the Neptunians did to e Plutonians, however, supposed that most eks were deposited from water. Theory may be stated shortly, as follows. la which comnose the present surface of the have been disintegrated and pulverized by the conaction of torrents and currents of water; and by the means these materials have been transported to the of the ocean. Here they have been consolidated, by time, and partly by the pressure of the water, but by the effects of subterranean heat. By the same more powerfully exerted, that is, by the expansive of volcanic heat, the strata thus formed have been d from the bottom of the ocean, to occupy the situunder which they now appear. Thus the strata are into different degrees of inclination to the horizon; broken and dislocated; or appear in nearly a vertiition, depending on the degree of force, or the point application. Sometimes, also, where the heat has ost intense, an entire fusion of the materials has been The rocks which are not stratified, or not comof layers, as granite, are supposed to have underomplete fusion, while those which consist of layers, a slate, are supposed only to have been softened by t. The same disintegration, and corrosion, and the cansportation to the sea, is constantly going on with to the present rocks, so that finally these materiI again be restored to the sea, to be again raised ts surface by volcanic fire, as before; and as the continents were formed by the destruction of anocks, so future continents will be formed in their y rocks now preparing for that purpose.-Brande's es of Geology. L. generally acknowledged at the present day, that 's theory will account for a much greater number logical phenomena than Werner's. It is impossir instance, to account for the present situation of ed rocks containing sea shells, unless we suppose, that the sea occupied the earth for ages, or that these vere formed under the ocean, and elevated by some force; and as we know that islands are thrown up he sea, by volcanic force, at the present day, it is able to attribute the same effect to the same cause, ly. GENERAL FORM AND CO Although in a popular s fa globe, yet science h igure is not that of a p period, the diameter at the poles. This differ but if we consider the the proportion of 304 ear the truth as the p dow. This allows the , and the two diamete Equitorial diameter, abou The Polar diameter This estimate is from Dr. Macculloch makes but we need not here There no two authors ag being a matter of no co This form of the ear would have taken had with a rapid motion ro ilustrated by fixing a ting it in motion. T or axis of motion, and cumference, or equato quence of the greater ence than at the centre Density of the Ed estimate the density of particular mountain. made an experiment on tous cliff, in order to on a suspended plum density of the whole e mate is from the authority of Daubuisson. och makes the difference somewhat greater, not here go into comparisons on a point o authors agree, the difference of a few miles ter of no consequence to our present purpose. a of the earth is precisely such a one as it taken had it been a homogenous semi-fluid Imotion round its axis. This form may be y fixing a ball of soft clay on a spindle and motion. The ball will be flattened at the poles otion, and elongated, or thrown out, at the ciror equator. This is obviously the consene greater centrifugal force at the circumferthe centre of motion. of the Earth. It has been attempted to e density of the whole earth from that of a mountain. For this purpose Dr. Maskelyne periment on mount Schihallien, a high precipin order to ascertain the force of its attraction, dad nlumm. with the view of deduais CONSTITUTION OF of the mountain. From such data it was found hean density of the earth was to that of the is 9 to 5; and from hence it was concluded that of the globe must be composed of substances sity was about double that of the mass of the But it was subsequently found that the speciof the mountain, an item in these calculations, stimated too high, and by the corrections made ayfair, the density of the earth obtained in this ound to be only 5. That is, the whole earth, ulk, is five times the weight of water. This hich is most generally received at the present sit necessary to suppose that the interior of the ch more dense than its surface; for the heaviest which we are acquainted has a density of only lightest about 24,while the specific gravity of s a little more than 1. The specific gravity of surface including the water, therefore, cannot bove 21. But the mean density of the whole 5, is more than double that of its surface, and nterior of the earth must have a greater density counterbalance this want of weight at the ese considerations, it has been supposed that r of the earth, instead of being composed of the surface, must consist of metallic substances. o been shown from mathematical calculations is a gradual increase of density towards the he earth, and hence it has been thought still able that its nucleus is of a metallic nature. THE Distribution of Sea and ce, with this view of the earth's structure, has ts density at the centre. If 5, 4 be taken as its ity and its superficial densities be assumed as 3, , 79; and 2, 60, then on the theory of the com, the density at the centre will be 13, 25; 14, 54; d 20, 10, respectively. The least of these is le the density of iron, and the greatest exceeds ld, being about equal to that of hammered e most ponderous of all known substances. philosophy and conjecture are alike useless bject, for in spite of both, we must remain oncerning the composition of the earth's as made a computation and valleys, like the hole ocean is iderably with respe contains. At the mou Beceive streams from the cannot be so fully satura thus diluted. There is quantity of salt whi pendently of any such c only by the analysis ferent specific graviti It will be remember which specific gravities hich is 1; and therefo atter any water conta gravity Dr. Marcet instituted ter from different parts ained the following re 1. "That the Southe the Northern, in the r 2. "That the mean n of Sea and Land. Nearly three fourths surface of the globe is covered by water. of the Pacific Ocean alone is estimated to greater than all the dry land with which we I-(Daubuisson.) st elevation of land is about 25,000 feet above e sea; but its greatest depression, being conwater, cannot be ascertained, and hence the ter which the oceans contain cannot be esny degree of accuracy. La Place, however, computation of the mean depth of the sea, e theory of the tides, by which he concludes t twelve miles. Concerning the bottom of now little more than that it consists of mouneys, like the surface of the land. This is asthe rocks, and islands which rise above the water, and the reefs and deep water, which exist alternately, below it. The sounding mariner not only detects this unevenness of e surface, but also the steep acclivities of its d the gradual risings of its sand banks. on and specific gravity of the Sea. The is composed of salt water, though it varies with respect to the quantity of solid matter At the mouths of rivers, and in bays which ms from the land, it is obvious that the water Fully saturated with salt, as it is where it is not There is also a difference wlth respect to of salt which different oceans contain, indeany such circumstance. This is ascertained, he analysis of their waters, but also by their ific gravities. remembered that the standard, or unity, by ic gravities are estimated, is distilled water, and therefore the greater the quantity of solid water contains, the greater will be its specific et instituted a series of experiments on sea waerent parts of the world, from which he ob llowing results and conclusions. the Southern Ocean contains more salt than n, in the ratio of 1.02919 to 1.02757." |