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In this address he announced his conviction that a great ice-period, due to a temporary oscillation of the temperature of the globe, had covered the surface of the earth with a sheet of ice, extending at least from the north pole to Central Europe and Asia.
Erratic materials and boulders transported from the north were scattered over its surface, and Agassiz found the illustrations for his lectures on this topic ready to his hand. Indeed, some of his finest lectures on the ice-period were given at Penikese. Nothing could be less artificial, more free from constraint or formality, than the intercourse between him and his companions of this summer.
But the vegetation which has succeeded the ice-period is of a different character, and one that could not have flourished on a soil that would nourish a more tropical growth. The soil we have now over the temperate zone is a grain-growing soil, one especially adapted to those plants most necessary to the higher domestic and social organizations of the human race.
As soon as the cave-man had escaped the threatening dangers of the long and shivering ice-period, and had put his house in order, he began to make certain things which he thought beautiful, although they were of no earthly use to him in his fight with the wild animals of the jungle.
On starting he had set before himself two subjects of inquiry. These were, first, the fresh-water fauna of Brazil, of the greater interest to him, because of the work on the Brazilian Fishes, with which his scientific career had opened; and second, her glacial history, for he believed that even these latitudes must have been, to a greater or less degree, included in the ice-period.
It is very noble and natural to wish that what has impressed us as true should also be recognized by those we love. . .I believe I have read and compared all that has been written for and against the ice-period, and also upon the transportation of boulders, whether pushed along or carried by floods or gliding over slopes.
The weeks he had spent there were all too short for the work he had hoped to do. Yet, trained as he was in glacial phenomena, even so cursory an observation satisfied him that in the southern, as in the northern hemisphere, the present glaciers are but a remnant of the ancient ice-period.
Since the beginning of the close of the ice-period the whole number in the range has perhaps never been greater than at present. A rough approximation to the average duration of these mountain lakes may be made from data already suggested, but I cannot stop here to present the subject in detail.
Rink show that in reality Greenland is a miniature picture of the ice-period. The immense number of icebergs breaking off and floating southward every summer gives us some idea of the annual waste and renewal of the ice.
In Vermont, the valley of the Winooski River retains ample traces of the local glacier by which it was formerly filled; and, indeed, throughout the Alleghany range, in its northeastern as well as its southern extension, we have various evidences of localized glaciers, which must have outlived the general ice-period for a longer or shorter time.
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