this office consisted simply in overseeing the various details of the work, and were not physically or mentally laborious; the hours were short and the labor did not produce mental exhaustion. Yet it did not leave him in quite as fresh condition as his work at Glasgow, and he was obliged to be very precise in the regulation of his life. He had early conceived a distaste for geology as involving too much the consideration of details and not giving due prominence to principles, but he had a special interest in the branch which bore upon the object of the particular study in which he was engaged—of surface geology or drift in its bearings on glacial and interglacial periods. He had begun his studies in this department before leaving the Andersonian College, and had made frequent excursions into the country in search of glacial phenomena. These excursions were continued with equal success after he went to Edinburgh; and Mr. James Bennie, who accompanied him on some of them, has left delightful accounts of them and of Mr. Croll, which are published in connection with Mr. Croll's correspondence.
In 1865 Mr. Croll suffered an affection which interfered seriously and permanently with his capacity for mental work. While bent down, assisting in putting a few tacks into a carpet, he felt a kind of twitch in his head. It did not affect his general health or impair his mental energy, but it was followed by a dull pain, which increased if he persisted in doing mental work for any length of time till it became unbearable; and he was never able afterward to keep his thoughts concentrated upon a single point as he had been before. Had it not been for this mishap, he says, all the private work which he was able to do during the twenty years that followed "might have easily been done, and would have been, in the course of two or three years." For a few years prior to the publication of Climate and Time it was with the greatest difficulty that he could manage to put together in one day as many sentences as would fill a half page of foolscap, and the appearance of the book was delayed on that account.
In the published correspondence of Mr. Croll appears a letter to him from Charles Darwin under date of July 19, 1871, stating that "Mr. Youmans [Prof. E. L. Youmans], of the United States, is very anxious to get a series of small monographs written by the most competent English authors on various subjects, to be published in the United States, and I suppose in England. Mr. Youmans is in some way connected with the great firm of Appletons in New York. He has asked me to name some of the most competent men, and I have thought that you would excuse my giving your name and this note as a kind of introduction. I should add that I do not know on what subject he wishes you to write. I do, however, know that some very good judges think
