Page:Popular Science Monthly Volume 44.djvu/554

540, have, it seems to us, placed the later Quaternary times at far too great a distance from the present. In the same way, the rate at which the elevation of the land took place having been estimated on the mean of two and a half feet in a century, would, if that scale were accepted, manifestly push back to a very remote distance even later geological changes.

The importance of determining these points more accurately became more evident when it was discovered that man existed with the extinct mammalia; and therefore upon the solution of the time-rate problem depended the determination of the antiquity of man upon the earth. Various have been the attempts since made; but, as they have almost all been made upon measurements based on the above-named scales, they necessarily involved a very free use of time. For long, geologists had held to the belief, prevailing half a century ago, that man could not have existed on the earth for more than five to six thousand years. When evidence was given, and at last accepted, to prove a higher antiquity, the uniformitarians were placed in the difficulty of proving too little or too much. If they adopted a short chronology, it would clash with the corner stone of their belief as to the age of the Quaternary deposits; if, on the other hand, they retained their belief in the great length of time they held to be necessary for the formation of the post or later glacial deposits, they would have to assign to man an antiquity which would clash sorely not only with their own previous belief, but also with that held on various grounds by other geologists and anthropologists.

The fetich of uniformity prevailed, the uniformitarians made volte-face to their former contention, and hesitated not to claim for man an antiquity going on for a million years. One old friend of ours, in a public lecture, even put in a claim for two millions, heedless of the cries of his unprepared audience to remind him of the rights of Adam. At a loss to prove their case by independent geological evidence, they found an unexpected ally in a novel and ingenious astronomical hypothesis, which apart from its connection with geology we will not contest. The object of the hypothesis was to show that there had been cycles, in which at times the position of the earth in its orbit was such as would cause a great lowering of the terrestrial temperature and give rise to recurring glacial periods. Here were offered the definite measures that geology failed to furnish, and which tallied too well with the time needed by the uniformitarians to be neglected. It was therefore eagerly adopted, and has since been prominent in geological literature. That the hypothesis, however, is not in accordance with the facts of geology has been abundantly shown both in America and in this country;