Basing his demonstration on this accumulated evidence, Agassiz proved that at one time glaciers had covered a large part of the now civilized world. The great boulders had been scooped up by them in their progress, and perhaps some thousands of years later had been dropped a hundred miles away by the melting ice-sheet. So also had the masses of gravel been carried far from their sources, to form strange new glacial deposits. And on the scarred and grooved rocks was the final evidence; for these deep scratches had surely been ground by the advancing glacier as it slowly and silently moved onward. “The idea that such phenomena were not restricted to regions where glaciers now are found, but that traces of glacial action could be seen over enormous tracts of the earth’s surface, perhaps including regions in the tropics, and that in countries now temperate there might be discovered, not only the remains of tropical fauna and flora, but also distinct indications of a period of arctic cold—this was as new as startling.” During the years of his professorship at Neuchâtel, Agassiz published many important contributions to scientific knowledge in those particular departments of natural science to which he had devoted himself. At the same time came also many honors, including offers of professorships from the universities of Geneva and Lausanne, and the award of the Wollaston Medal by the Geographical Society of London. But the second period in Agassiz’s life was drawing to a close: a great country beyond the Atlantic would soon be ready to receive him. Agassiz, the student and now the discoverer, was about to begin his final great activity as the pioneer and teacher of natural history to a strange people in a foreign land. Each year at Neuchâtel had plunged Agassiz deeper and deeper into debt; his situation had passed from bad to well-nigh hopeless. Then, unexpectedly, help was offered. The King of Prussia offered him three thousand dollars, to be spent in travel for scientific purposes; and at the same time came an invitation from the Lowell Institute of Boston to visit the United States. Agassiz could not refuse. It was a solution of all his immediate difficulties; a wide horizon in the eager young republic spread before him. In September, 1846, Agassiz sailed for Boston. He had left behind him all that is wealth to a scientific man. Books and collections were the tools of his trade; in his fellow naturalists he had found help and inspiration. In the United States bountiful nature had provided a fertile and unexplored field, but here he must work alone. “He came, perhaps, in a spirit of adventure and of curiosity; but he stayed because he loved a country where new things could be built up; where he could think and speak as he pleased; and where his ceaseless activity would be considered of high quality.”