riable, and often of no great, extent. If marine, an alteration in › sea bottom will prove fatal to many. If terrestrial, an increase altitude, the conversion of dry land into marshes and lakes, or lakes and marshes into meadow and arid loamy soil, will cometely alter the flora and fauna of the district in question. Look to any estuary or rocky pool along the shore of the ocean, varming with testacea, and crustacea; every bowlder incrusted ith corallines; the rocks carpeted all over with fuci, waving with very ripple their long graceful branches, or smoothing and polishng their sides in the violent currents; creeping things, too, innuerable shy stealthy creatures, darting amid the shingle, or urrowing in the sands; and the finny tribes, of all forms, glancng and sparkling like living gems in the dark green thickets. This is one description only of tens of thousands of such phenonena around the islands of Great Britain. An elevation of a few eet, and what myriads of animals, whose only habitat are these ocean caves, would perish, and their races be forever blotted from the things that were! These shores have witnessed many such upheavals. Not a plain, hill, or rock, in the whole continent of Europe, but once formed the bed of the sea. Even now, what a vast influence does mineralogical structure alone exercise over the economy of life, both as to the number of individuals and the character of species frequenting particular localities. Trees as well as plants have an adaptation to certain kinds of soil, and once firmly rooted, birds, insects, and creeping things, will also resort thither in quest of shelter or of food. Aquatic fowl, the waders and swimmers of our sea-shores, have their favorite haunt among the breakers or calm bays, whose submarine rocks furnish pasturage and shelter to molluscs, crustaceans, and fishes; while, again, over the marshy, the oozy, the sandy, the gravelly, or the rocky beach, other families, both terrestrial and marine, maintain their respective ascendency.

M. Agassiz is just now pursuing his favorite researches in exploring the lakes and rivers of America, where he has already detected many things new and old to enlighten the western savans in the boundless riches of their mighty dominions. He has succeeded in capturing, on Lake Superior, species of fishes hitherto

unnamed. He has likewise been able to dredge up from the same deep waters, specimens of the garpike (Lepidosteus), whose representatives have been found in the oldest palæozoic deposits, and in the deposits of all succeeding times. Suppose these lakes to be suddenly drained of their waters—and which, according to the chronometrical details of Niagara, must one day come to passand many species of animals and plants would cease to exist, not merely by the violence of the action, but by the simple alteration of the aqueous character of the districts. Many animals, indeed, will be able to escape, and to betake themselves to other localities amidst slow or even rapid superficial changes. The camels and antelopes of the desert may sink under the sirocco and be buried in the sand; but, in other circumstances, they will be able to bear up and carry themselves to fertile lands, as the steady, irresistible march of the sand-flood invades their former pastures. The Sahara of Africa has been gradually extending and widening in its desolating sterility, until it now covers a region of about 582,000 square miles; how many, in consequence, of the vegetable and animal races, have thus been deprived of their appropriate nutriment, and become extinct? How many examples of similar de vastations, but upon a far greater scale, does almost every one of the geological epochs furnish? The central region of France abounded with lakes, attracting to their arborescent banks the huge pachyderms of the tertiary age, when the Auvergne cones blazed out, pouring floods of lava over lake, marsh, and plain; and thus obliterating and silting up entire races, the great and the small, terrestrial and lacustrine, and now constituting the pictorial wonders of the age that produced, and the convulsions that destroyed them.

There is reason to believe that species in the ancient world were possessed of a wider geographical range than in after periods. But the causes of extirpation were also of wider operation. The old formations are all greater than the new, receding in extent as they descend in time. And if we are to regard alterations of climate, changes in the constituents of the atmosphere, subsidence of land and elevation of sea-bottom, intrusion of igneous rocks, the escape and circulation of noxious gaseous matter, as among

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causes which have led to the extinction of the successive ganic tribes in the several geological epochs, so do we find the Fects approximating to a scale of corresponding magnitude. But ie real terms and boundaries of all are in the hands of Him who ade them. We see but a part, and know only in part, of the econdary means of destruction.

CHAPTER V.

TIME, AND THE GEOLOGICAL EPOCHS.

THE speculations of geology respecting the arrangement and position of the mineral masses of the earth are matters of direct observation, falling immediately under the cognizance of the senses, and whose verifications are both numerous and conclusive. But a question thereupon arises which is not so easily dealt with, namely, as to the periods of time that have elapsed during the various successive epochs or formations described. Looking at the current operations of the laws of nature, and supposing their uniformity in past ages, a scale of increment is laid down for the several deposits of which the earth's crust is composed. An approximation is made as to the number of years required for each, and the result is, that the geological estimate embraces an inconceivably lengthened and bewildering series. The calculation proceeds not by hundreds, or thousands, but by millions of the terms of our numerical notation: and, as the fossiliferous strata alone are reckoned at about seven or eight miles in thickness, the time that has elapsed since the first appearance of life upon the planet, has also been made a matter of measurement. Accuracy as to any precise definite amount, is not, indeed, pretended; but no estimate, it is said, made upon purely geological data, falls short of vast enormous periods, which will only bear to be compared with the cycles of astronomical phenomena, and not with the brief fleeting days of man's existence.

What account, then, is to be made of this reckoning according to the popular opinions respecting the origin of the world? Will it be accepted by the Christian, who confides in the Mosaic chronology of the work of creation? What is that chronology? Can the geological and the sacred be compared or reconciled with one another?

I. There is one important deduction to be established from ese investigations which meets us at the threshold of the inquiry, amely, that geology clearly and distinctly shows there is a EGINNING to the course of creation as respects the crust of the earth nd its organic forms of life. The stratified rocks all manifest sucession in their order of deposition, and, therefore, also succession a time. Some are prior to and older in formation than others; nd all of every class and quality, demonstrate principles of arangement in conformity with law and design. We never, for example, get back to a period, however deep we go into the inteior, in which we find the matter of the earth assuming, as it were, different modes of existence, or arranging itself according to affinities of which we have no experience. Over every material substance, the rocks of the oldest as of the newest formation, the same physical forces are seen to be operative. The granites, with all the molten amorphous masses of every age, are composed of ingredients brought together and aggregated in proportional quantities, and according to definite principles of attraction. But throughout the whole series and succession of deposits, we never come to a point at which matter has been formless, or free from the operation of law, endlessly quiescent, or when no controlling designing hand was rendering it plastic and obedient to its will.As with the arrangements of matter, therefore, so likewise with its origin. We revert in both cases to a necessarily prior cause. And geology, vast and inconceivably great as may be its cycles, proclaims over all its past antecedents and depths of accumulation, that TIME, not eternity, is indelibly recorded.

This truth is rendered still more apparent and intelligible, when we consider the various families of plants and animals of which the earth has been the theater. These organic structures at once

speak to the mind of creative interference. No principle that we know of inherent in nature could, of itself, originate these forms. The first thing of life indicates an intelligent Creator. But epoch after epoch passes away, and along with them their living tribes generally perish. Succeeding races, of different characters and habits, are called into existence. The earth is again peopledagain to be swept of all its garniture-the land and ocean to change places-creatures of another mold, suited to both, again