Imposing as the modern glaciers are, they are not so huge as were some that once existed.  For instance, Mr. Whymper says: 

“At some very remote period the Valley of Aosta was occupied by a vast glacier, which flowed down its entire length from Mont Blanc to the plain of Piedmont, remained stationary, or nearly so, at its mouth for many centuries, and deposited there enormous masses of debris.  The length of this glacier exceeded eighty miles, and it drained a basin twenty-five to thirty-five miles across, bounded by the highest mountains in the Alps.  The great peaks rose several thousand feet above the glaciers, and then, as now, shattered by sun and frost, poured down their showers of rocks and stones, in witness of which there are the immense piles of angular fragments that constitute the moraines of Ivrea.

“The moraines around Ivrea are of extraordinary dimensions.  That which was on the left bank of the glacier is about thirteen miles long, and in some places rises to a height of two thousand one hundred and thirty feet above the floor of the valley!  The terminal moraines (those which are pushed in front of the glaciers) cover something like twenty square miles of country.  At the mouth of the Valley of Aosta, the thickness of the glacier must have been at least two thousand feet, and its width, at that part, five miles and A quarter.”

It is not easy to get at a comprehension of a mass of ice like that.  If one could cleave off the butt end of such a glacier—­an oblong block two or three miles wide by five and a quarter long and two thousand feet thick —­he could completely hide the city of New York under it, and Trinity steeple would only stick up into it relatively as far as a shingle-nail would stick up into the bottom of a Saratoga trunk.

“The boulders from Mont Blanc, upon the plain below Ivrea, assure us that the glacier which transported them existed for a prodigious length of time.  Their present distance from the cliffs from which they were derived is about 420,000 feet, and if we assume that they traveled at the rate of 400 feet per annum, their journey must have occupied them no less than 1,055 years!  In all probability they did not travel so fast.”

Glaciers are sometimes hurried out of their characteristic snail-pace.  A marvelous spectacle is presented then.  Mr. Whymper refers to a case which occurred in Iceland in 1721: 

“It seems that in the neighborhood of the mountain Kotlugja, large bodies of water formed underneath, or within the glaciers (either on account of the interior heat of the earth, or from other causes), and at length acquired irresistible power, tore the glaciers from their mooring on the land, and swept them over every obstacle into the sea.  Prodigious masses of ice were thus borne for a distance of about ten miles