The Ice Age in North America, and Its Bearings Upon the Antiquity of Man (Paperback)

This historic book may have numerous typos, missing text, images, or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1889. Not illustrated. Excerpt: ... CHAPTER XX. THE DATE OF THE GLACIAL PERIOD. Two causes have combined in recent years to favor erroneous calculations concerning glacial chronology. Of these, the first has been the almost unquestioned acceptance of the astronomical theory subjected to examination in the preceding chapter. If Mr. Croll's theory of the cause of the Glacial epoch is correct, then we should no longer speak of an ice age, but of a succession of such ages, whose dates could be readily determined from a table showing the periods of highest eccentricity in the earth's orbit. According to this table, the modern period most favorable to, the production of a glacial epoch began about two hundred and forty thousand years ago and ended about seventy thousand years ago. The whole intervening time was one of high eccentricity, when, during the recurring intervals in which the winters occurred at aphelion, the excess of winter over summer ranged from fourteen to twenty-six days, and the intensity of the heat received from the sun during those aphelion winters was ten per cent less than at the present time. During the time intervening between seventy thousand and two hundred and forty thousand years ago, there occurred, therefore, according to this theory, a succession of glacial and interglacial periods in which geologists and archaeologists are invited to distribute their remarkable discoveries concerning glacial man. Undue confidence in this theory has had no small influence in diverting attention from the more legitimate lines of investigation. A second source of error has been an incorrect interpretation of Lyell's principle of uniformity in Nature's operations. This has led to an exaggerated estimate of everything pertaining to geological time. There is a prevalent popular impress...