On one occasion, happening to meet a number of students at the corner of University Building, one of them was bold enough to say to him: "Prof. Agassiz, would you be so good as to explain to us the difference between the stone of this building and that of Boylston Hall? We know that they are both granite, but they do not look alike." Agassiz was delighted, and entertained them with a brief lecture on primeval rocks and the crust of the earth's surface. He told them that Boylston Hall was made of syenite; that most of the stone called granite in New England was syenite, and if they wanted to see genuine granite they should go to the tops of the White Mountains. Then looking at his watch he said: "Ah, I see I am late! Good day, my friends; and I hope we shall all meet again." So off he went, leaving each of his hearers with the embryonic germ of a scientific interest in his mind. Longfellow tells in his diary how Agassiz came to him when his health broke down and wept. "I cannot work any longer," he said; and when he could not work he was miserable. The trouble that afflicted him was congestion of the base of the brain, a disorder that is not caused so frequently by overwork as by mental emotion. His cure by Dr. Edward H. Clarke, by the use of bromides and the application of ice, was considered a remarkable one at the time; but five years later the disorder returned again and cost him his life. He believed that the Laurentian Mountains, north of the St. Lawrence River, was the first land which showed itself above the waste of waters with which the earth was originally surmounted.