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314 onsidered which was consumed during this phase of its life, and the time which elapsed during its prolonged sojourn at Ivrea, and the time which passed before it attained its maximum dimensions, it must be conceded that the period of 1055 years was, in all probability, only a small portion of the epoch during which the Valley of Aosta sustained the grinding of this enormous mass of ice.

Let us confine ourselves to certainties. Here, then, was a glacier which flowed down the Valley of Aosta for more than a thousand years, having a thickness of 2000 feet, a width of several miles, and a length of eighty miles. The existing glaciers of the Alps do not approach these dimensions, and even in the period when the ice-streams of Europe had so great an extension there were very few which surpassed them. Still fewer, perhaps, existed for so long a period, and there are probably only one or two—such as the ancient glacier of the Rhone—which have received as much attention and have been as carefully studied. For these reasons it seems to me to be more advantageous to refer to it than to instances more imperfectly known and more open to doubt; and I have selected it, on account of these reasons, as a valley which should afford strong testimony in support of the theories which assert that the valleys and many of the lake-basins of the Alps have been excavated by glaciers.

The latter of these two theories was communicated to the Geological Society, by Professor Ramsay, on March 5, 1862. It received much attention, and excited much criticism. I am not aware that Professor Ramsay replied to any of his critics, excepting Sir Roderick Murchison and Sir Charles Lyell. But in answer to the objections which were raised against the reception of his theory