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 the _causes_ which have led to the extinction of the successive organic tribes in the several geological epochs, so do we find the _effects_ approximating to a scale of corresponding magnitude. But the real terms and boundaries of all are in the hands of Him who made them. We see but a part, and know only in part, of the secondary 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?