Few people realise either the rapidity with which geological changes are now proceeding or the small amount of change which might produce a Glacial period, and fewer still have an adequate conception of how long a period a million years is, and how much present geological agencies would accomplish in that time. At the present rate at which erosive agencies are now acting upon the Alps, their dimensions would be reduced one half in a million years. At the present rate of the recession of the Falls of St. Anthony, the whole gorge from St. Louis to Minneapolis would have been produced in a million years. A river lowering its bed a foot in a thousand years would produce a cañon a thousand feet deep in a million years. If we suppose the Glacial period to have been brought about by an elevation of land in northern America and northern Europe, proceeding at the rate of three feet a century, which is that now taking place in some portions of Scandinavia, this would amount to three thousand feet in one hundred thousand years, and that is probably all, and even more than all, which is needed. One hundred thousand years, therefore, or even less, might easily include both the slow coming on of the Glacial period and its rapid close. Prestwich estimates that the ice now floating away from Greenland as icebergs is sufficient if accumulating on a land-surface to extend the borders of a continental glacier about four hundred and fifty feet a year, or one mile in twelve years, one hundred miles in twelve hundred years, and seven hundred miles (about the limit of glacial transportation in America) in less than ten thousand years. After making all reasonable allowances, therefore, Prestwich's conclusion that twenty-five thousand years is ample time to allow to the reign of the ice of the Glacial period cannot be regarded as by any means incredible or, on _a priori_ grounds, improbable. APPENDIX. THE TERTIARY MAN. By Professor Henry W. Haynes. "It must not be imagined that it is in any way proved that the Palæolithic man was the first human being that existed. We must be prepared to wait, however, for further and better authenticated discoveries before carrying his existence back in time further than the Pleistocene or post-Tertiary period."[EW] This was the position assumed more than twelve years ago by the eminent English geologist and archæologist, Dr. John Evans, and it was still maintained in his address before the Anthropological Section of the British Association on September 18, 1890. I believe that the study of all the evidence in favor of the existence of the Tertiary man that has been brought forward down to the present time will leave the question in precisely the same state of uncertainty. [Footnote EW: _A Few Words on Tertiary Man_, Trans, of Hertfordshire Nat. Hist. Soc, vol. i, p. 150.]