Observing the present gradual retreat of those ice remnants which remain mere shreds and patches of the ancient fields, it seems at first sight likely that the extension and recession of the great glaciers took place with exceeding slowness. Measured in terms of human life, in the manner in which we gauge matters of man's history, this process was doubtless slow. There are reasons, however, to believe that the coming and going were, in a geological sense, swift; they may have, indeed, been for a part of the time of startling rapidity. Going back to the time of geological yesterday, before the ice began its development in the northern hemisphere, all the evidence we can find appears to indicate a temperate climate extending far toward the north pole. The Miocene deposits found within twelve degrees, or a little more than seven hundred miles, of the north pole, and fairly within the realm of lowest temperature which now exists on the earth, show by the plant remains which they contain that the conditions permitted the growth of forests, the plants having a tolerably close resemblance to those which now freely develop in the southern portion of the Mississippi Valley. Among them there are species which had the habit of retaining their broad, rather soft leaves throughout the winter season. The climate appears, in a word, to have been one where the mean annual temperature must have been thirty degrees or more higher than the present average of that realm. Although such conditions near the sea level are not inconsistent with the supposition that glaciers existed in the higher mountains of the north, they clearly deny the possibility of the realm being occupied by continental glaciers. Although the Pliocene deposits formed in high latitudes have to a great extent been swept away by the subsequent glacial wearing, they indicate by their fossils a climatal change in the direction of greater cold. We trace this change, though obscurely, in a progressive manner to a point where the records are interrupted, and the next interpretable indication we have is that the ice sheet had extended to somewhere near the limits which we have noted. We are then driven to seek what we can concerning the sojourn of the ice on the land by the amount of wearing which it has inflicted upon the areas which it occupied. This evidence has a certain, though, as we shall see, a limited value.