Agassiz himself was necessarily often absent, for the maintenance of the little colonydepended in great degree upon his exertions. During the winter of 1847, while continuing his lectures in Boston and its vicinity, he lectured in other places also. It is difficult to track his course at this time; but during the winters of 1847 and 1848 he lectured in all the large eastern cities, New York, Albany, Philadelphia, and Charleston, S.C. Everywhere he drew large crowds, and in those days his courses of lectures were rarely allowed to close without some public expression of gratitude and appreciation from the listeners. Among his papers are preserved several sets of resolutions from medical and scientific societies, from classes of students, and from miscellaneous audiences, attesting the enthusiasm awakened by his instruction. What he earned in this way enabled him to carry on his work and support his assistants. Still, the strain upon his strength, combined with all that he was doing beside in purely scientific work, was severe, and before the twelvemonth was out he was seriously ill. At this time Dr. B.E. Cotting, a physician whose position as curator of the Lowell Institute had brought him into contact with Agassiz, took him home to his house in the country, where he tended him through some weeks of tedious illness, hastening his convalescence by excursions in all the neighboring country, from which they returned laden with specimens,--plants, birds, etc. In this hospitable home he passed his fortieth birthday, the first in this country. His host found him standing thoughtful and abstracted by the window. "Why so sad?" he asked. "That I am so old, and have done so little," was the answer. After a few weeks he was able to return to his work, and the next letter gives some idea of his observations, especially upon the traces of glacial action in the immediate vicinity of Boston and upon the shores of Massachusetts Bay. Indeed, he never lost sight of these features, which had caught his attention the moment he landed on the continent. In one of his later lectures he gives a striking account of this first impression. "In the autumn of 1846," he says, "six years after my visit to Great Britain in search of glaciers, I sailed for America. When the steamer stopped at Halifax, eager to set foot on the new continent so full of promise for me, I sprang on shore and started at a brisk pace for the heights above the landing. On the first undisturbed ground, after leaving the town, I was met by the familiar signs, the polished surfaces, the furrows and scratches, the LINE ENGRAVING, so well known in the Old World; and I became convinced of what I had already anticipated as the logical sequence of my previous investigations, that here also this great agent had been at work." The incident seems a very natural introduction to the following letter, written a few months later:-- TO ELIE DE BEAUMONT. BOSTON, August 31, 1847.