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beautiful diversity of mountain and valley, of hill and dale, of streamlet and river, of lake and ocean. We study it in relation to general physics and physical geography—the latter having first unfolded its principles and gave rise to its earliest development as a science.

In directing our enquiries to, the elementary constitution of the rocks which form the upper layers of the body of the earth, their lithological characters and the influence which one may have exercised in the formation of another, our results become intimately associated with those of chemistry and mineralogy.

If we extend our observation again, to a survey of the organic remains embedded in these mineral masses-to the local influence or universality of the causes which operated during their existence-to the relative ages of these rocks as characterized by differences of genera or species in their faunas and floras, we discover relations which form the subordinate ground-work of modern classifications in geology, and blend it intimately with botany and zoology.

Directing our enquiries to the chemical constitution of these diversified masses, to the changes which occur in them from atmospheric agencies- the variety of soil to which their decomposition gives rise the influence which their elevation or depression-their absorption or radiation of heat-their permeability or impermeability to moisture, exercises on the transparency, density and temperature of the atmosphere, and consequently, their influence on climate, we give to geology a still wider range, and study it in that philosophical method which enables us to trace the influence of the inorganic world upon the development of organized forms of being, and thus indirectly associates it with the science of life.

Lastly, we may survey these mineral masses in their distribution, as modified and rendered available to the arts and commerce of the world; their influence in varying the forms of human industry, giving rise to national peculiarities and to national wealth, and in aiding the regular advancement of kingdoms and nations in the march of civilization and refinement. In this view it becomes more practical in its results, and intimately identifies itself with the principles of political economy and enlightened legislation.

It will be perceived from this general summary of the leading objects of geological enquiry, that as a science it is almost umlimited in extent; and involves in its considerations questions of the highest moment, and of the deepest philosophical interest.

The earth, as is well known, is an oblate spheriod, being compressed at the poles and elevated to a corresponding extent at the equator. This difference between its polar and equatorial diameter, is considered a conclusive proof that at one time it was in a state of fusion-its ellipticity being the result of a centrifugal force operating on it at the time. Its loss of heat, and consequent contraction in cooling, must have had a powerful agency in producing the irregularities of its surface. Since it was prepared for the abode of man and the present races of animals, it has experienced no appreciable loss of heat or change in its density.

Modern calculations, founded on geodesical measurements, give it an ellipticity of 1-299, being a difference of about 23 1-5 geographical miles between its polar and equatorial diameter.

This spheroidal figure of the earth is not uniform in its outline, but is interrupted by lofty mountains and elevated table lands, by deep valleys and water-worn channels. Were the waters which fill its profoundest depressions and constitute oceans and inland seas, removed, its continental masses and islands, would appear as elevated table lands and mountain chains, and the irregularity and boldness of its form would be materially increased

These continental masses and islands form the smaller portion of its surface in contact with the atmosphere, or the ærial ocean which surrounds it. The relative proportion of the land to the water being estimated at about as 1 to 2.8, or, according to Rigaud, as 1 to 2.7. The islands, it is estimated, would form only about 1-23 part of the continents: and, by refering to the globe, it will be found that the northern contains three times as much land as the southern hemisphere, and that the major axes, or lines of elevation above the sea, on the two continents, are opposite in direction.

The mean density of the earth has been recently estimated at 5.44, distilled water being 1. The strata near the surface giving only a density of 2.7, and when taken with that of the ocean, gives a density of only 1.6. These estimates have led to the important inference of the greater density of the interior portions of the globe.

The temperature of the earth is partly derived from the sun, while it has temperature of its own, which is supposed to be the residum left after it had cooled by radiating its heat into the space which surrounds it. Its own internal heat exercises no influence on the temperature at the surface, for, reaching a line below the surface, called the line of no variation, it is uniform at all seasons. This line of no variation is only a foot below the surface at the equator, and is found to increase in depth towards the poles. From this line of no variation the temperature of the earth increases as we descend towards its centre. Accurate measurements have established the fact that for every 54 feet of descent there is an increase of one degree of Fahrenheit's scale. The arithmetical ratio of these numbers would give a temperature sufficient to melt granite at the distance of twentyone miles below the surface. From this regular increase in temperature it has been infered by some that the centre of the earth is still in a state of fusion. But this, it is obvious, can only be received as a plausible conjecture; for, so far as the interior of the earth is concerned, we cannot determine anything except its temperature and its density. The labors of the geologist are limited to its surface or the various masses which are presented by the disruptions in its external crust. By examining the arrangement of these as presented in the deepest mines, which are only about one-third of a mile below the level of the ocean, and on the flanks of the highest mountain ranges, which do not exceed six miles in elevation, and

by comparing observations made at different and distant points on the earth, a reg-. ularity and order in the relations of these masses have been found to exist, which scarcely could have been anticipated in the midst of such seeming confusion Though this field of observation is exceedingly limited when compared with the whole diameter of the earth, it has proved amply sufficient to give us a knowledge of its constitution and the series of revolutions by which its gradual development to its present condition has been characterized.

The varying constitution of these masses-the regularity of their arrangement in a successive series, or their order of super-position, one above another-the organic remains which have been found in them, and which defines their relative ages, have all been carefully studied, and have resulted in a more definite and natural division in their classification.

The general divisions established among the different formations have been founded either on their relative ages or their origin. The subdivisions into orders of these classes, seems to have been much more arbitrary, for the principal groups in each have been designated in some instances by terms expressive of the constitution of some prominent rock in the formation, and in others by the names of countries or places in which they are found distributed to the greatest extent. Following the arrangement into classes and principal groups most commonly received, we will refer to each in succession, proceeding from below upwards.

1. PLUTONIC ROCKS.-This division includes only a part of the rocks which are supposed to be of igneous origin. The different varieties of granite, and a few porphyries are found to constitute the more solid foundation on which all the other formations seem to repose. Granite is massive in form, and presents a rough crystaline texture when fractured; it is not divisible into layers or strata, and it shows the appearances of a mass which has cooled from a state of fusion, under circumstances of great pressure, and entire occlusion from the atmosphere. It seems not to have been erupted or ejected through fissures in other formations so as to have carried with it and cemented small fragments of these, as we find in the breccias of volcanic origin. Though often found filling chasms in other rocks, and effecting changes upon them similar to the changes effected by volcanic action, it seems no where to present the appearance of having been elevated by a violent or turbulent expansive force.

2. THE METAMORPHIC ROCKS.-This division embraces the lower stratified rocks, and is subdivided into the gneiss mica slate, primary limestone, tolcose slate, hornblende slate, quarts rock and clay slate. Several members of this formation, like granite, are crystaline in their texture, but present planes of stratification, which show that they were formed under different circumstances. It is supposed that they were deposited in the more ancient seas, and having undergone fusion, subsequently, under the weight of the superincumbent waters, assumed their slaty or schistous character, and their crystaline structure. This view is rendered extremely plausible, if not certain, from the fact that such transforma

tions have been discovered where the lava of volcanoes have come in contact with argillaceous and calcareous rocks of more recent formation, and that modern chemistry has effected precisely similar transformations on the same materials..

In classifying rocks according to their origin, it is evident that these metamorphic rocks belong properly to the aqueous or sedimentary division, though the circumstances attending their formation were somewhat different from that comparative state of quietude which accompanied the deposition of the fossiliferous strata found reposing upon them. That the surface of the granite on which they rest was subject to greater disturbances may be inferred from their more frequent intercalation than the fossiliferous rocks, while the agency of heat may be traced, not less in their crystaline structure, than in the manner in which they have sometimes been bent, or contorted, and folded upon themselves.

3. STRATIFIED FOSSILIFEROUS ROCKS (the aqueous rock of Mr. Lyell.)—As indicated by its name, this great division of rocks embraces all the formations which contain the remains of animals or plants embedded in their substance; and, consequently, includes the transition secondary and tertiary formations of the improved Wernerian system, or the Silurian, Devonian, Carboniferous, Permian, Triassic, or new red sandstone, Lias, Oolitic, Wealden and Tertiary groups of more modern classifications, which we have adopted, as being at present most generally received. The formations constituting this extensive division, differ in some respects from the plutonic and the metamorphic rocks-and their transition or gradual change from the metamorphic to a well characterized fossilifferous state is often obscure. The entire series is formed of argillaceous calcareous and arenenaceous strata, often several thousand feet thick, presenting a compact and earthy structure, but seldom any evidences of having been regularly crystalized. These strata are often divisible into layers or beds commonly called shales or schists, which are not so thin and compact in the upper as in the lower series. The inferior group in this division embraces the lower Silurian rocks; these are stratified, and present the evidences of having been deposited at a period characterized by a state of greater tranquility than that of the metamorphic rocks. Interculations, however, are observed here, which prove that revolutions formerly so frequent in the meIt is in the lower tamorphic rocks, became less frequent in their occurrence. strata of this formation that the first remains of organic life have been discovered. A few fucoids polyparia and brachiopida are found in the lower beds of the Cambrian or lower Silurian. As we ascend in the series of formations, these remains of a former world increase in number, and offer us many new genera and species. Fishes, the first family of vertebrated animals, appear for the first time in the upper Silurian, and receive their full development in the Devonian or old red sandstone formation. These types, so profusely multiplied in the Silurian and Devonian, undergo an almost entire extinction in the Permian and Triassic series, and give place to new genera and species. It is in the Permian that we first find the remains of the Thecodont and other Saurians, (huge vertebrated an

imals) partaking of the nature of both fishes and reptiles, which receive their greatest development in the lias. The foot prints of birds are found for the first time in the Triassic or upper new red sandstone.

In the lower Oolite two mammiferous quadrupeds, of the marsupial or opossum tribe are found, as the first and only representatives of this class now so extensive. Above the cretaceous or chalk in the Paris Basin, Anaplotheroid and other races make their appearance, become extinct and give place to the Mastodon, the Elephant, the Megalonix and others, which are found in the alluvial deposits on the surface. Among all these remains no traces of man or his works have been found, in a fossilized state, in any formation which is not evidently cotemporaneous.

From this it will be perceived that in the types of animal life, the creation has been successive from the less to the more perfect forms of organization. The 'same may said of the vegetable world. The cellular or agamic were succeeded by the endogenous; and these by the cogengenous, or phenogamous families, which at present clothe and beautify the surface of the earth. It appears, then, that the types of the organized forms found in a fossilized state, have been preserved till the present time, but the genera and species have, in most instances, been destroyed by the revolutions which have marked the past history of the earth. We have given greater extension to this notice of the fossiliferous rocks, because two of its groups, the Carboniferous and Silurian occupy so prominent a place in the geology of the west. The Silurian system is well displayed, and attains its greatest power in the State of New York. Many of its strata thin out in proceeding towards the west, where the carboniferous (not found in the State just mentioned,) attains its greatest development. In the subjoined table, we have endeavored to present at a glance, the equivalency, or the parallelism of the formations of Europe, with those of New York and the Western States.

It yet remains to notice one more division, or class of rocks:

4. VOLCANIC ROCKS, embracing basalt, trachyte, diorite, and other igneous rocks, are of limited extent, when compared with the fossiliferous strata to which we have referred. They are found principally in the vicinity of active or extinct volcanoes in many parts of the world. Though of igneous origin, they differ from Plutonic Rocks in being often formed of breccias and tufas, and in presenting a less crystaline and a more porous or vessicular structure. They occasionally penetrate and fill up fissures and chasms in the Plutonic and Metamorphic Rocks, and then constitute what are termed dykes. Sometimes they are found intervening between fossiliferous strata, but most frequently penetrating all the other formations in the earth's crust, capping or over-spreading them at the surface.

The peculiarities in the structure of some volcanic rocks, are not only sufficient to distinguish them from those belonging to the plutonic, but prove that though identical in their igneous origin, the circumstances which prevailed at the period of their formation were essentially different. The granites seem to have been formed under great pressure, excluded from the influence of the atmosphere and

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