On the fourth of November of that year I read a paper before the Geological Society of London, containing a summary of the scientific results of that excursion, which I had extended with the same success to Ireland and parts of England. This paper was followed by one from Dr. Buckland himself, containing an account of his own observations, and another from Lyell on the same subject. From that time, the investigation of glaciers in regions where they no longer occur has been carried to almost every part of the globe. Before giving a more special account of this expedition, I will say a word of the mass of facts which I had brought from my Alpine researches, on which my own convictions were founded, and which seemed to Buckland worthy of careful consideration. To explain these more fully to my readers, I must leave the Scotch hills for a while, and beg them to return with me to Switzerland once more. Thus far I have spoken chiefly of the advance of glaciers, and very justly, since they are in constant onward motion, being kept within their limits only by a waste at their lower extremity proportionate to their advance. But in considering the past history of glaciers, we must think of their changes as retrograde, not progressive movements; since, if the glacial theory be true, a great mass of ice, of which the present glaciers are but the remnants, formerly spread over the whole Northern hemisphere, and has gradually disappeared, until now no traces of it are to be found, except in the Arctic regions and in lofty mountain-ranges. Every terminal moraine, such as I described in the last article, is the retreating footprint of some glacier, as it slowly yielded its possession of the plain, and betook itself to the mountains; wherever we find one of these ancient semicircular walls of unusual size, there we may be sure the glacier resolutely set its icy foot, disputing the ground inch by inch, while heat and cold strove for the mastery. There may have been a succession of cold summers, or, if now and then a warmer summer intervened, a colder one followed, so that the glacier regained the next year the ground it had lost during the preceding one, thus continuing to oscillate for a number of years along the same line, and adding constantly to the _debris_ collected at its extremity. Wherever such oscillations and pauses in the retreat of the glacier occurred, all the materials annually brought down to its terminus were collected; and when it finally disappeared from that point, it left a wall to mark its temporary resting-place.