severe opponents of the exactness of my observations, namely, M. Studer, who accompanied me on a part of these excursions. . . The winter of 1840 was fully occupied by the preparation for the publication of the "Etudes sur les Glaciers," which appeared before the year was out, accompanied by an atlas of thirty-two plates. The volume of text consisted of an historical resume of all that had previously been done in the study of glaciers, followed by an account of the observations of Agassiz and his companions during the last three or four years upon the glaciers of the Alps. Their structure, external aspect, needles, tables, perched blocks, gravel cones, rifts, and crevasses, as well as their movements, mode of formation, and internal temperature, were treated in succession. But the most interesting chapters, from the author's own point of view, and those which were most novel for his readers, were the concluding ones upon the ancient extension of the Swiss glaciers, and upon the former existence of an immense, unbroken sheet of ice, which had once covered the whole northern hemisphere. No one before had drawn such vast conclusions from the local phenomena of the Alpine valleys. "The surface of Europe," says Agassiz, "adorned before by a tropical vegetation and inhabited by troops of large elephants, enormous hippopotami, and gigantic carnivora, was suddenly buried under a vast mantle of ice, covering alike plains, lakes, seas and plateaus. Upon the life and movement of a powerful creation fell the silence of death. Springs paused, rivers ceased to flow, the rays of the sun, rising upon this frozen shore (if, indeed, it was reached by them), were met only by the breath of the winter from the north and the thunders of the crevasses as they opened across the surface of this icy sea."* (* "Etudes sur les Glaciers" Chapter 8 page 35.) The author goes on to state that on the breaking up of this universal shroud the ice must have lingered longest in mountainous strongholds, and that all these fastnesses of retreat became, as the Alps are now, centres of distribution for the broken debris and rocky fragments which are found scattered with a kind of regularity along certain lines, and over given areas in northern and central Europe. How he followed out this idea in his subsequent investigations will be seen hereafter. CHAPTER 10. 1840-1842: AGE 33-35. Summer Station on the Glacier of the Aar. Hotel des Neuchatelois. Members of the Party. Work on the Glacier. Ascent of the Strahleck and the Siedelhorn. Visit to England. Search for Glacial Remains in Great Britain. Roads of Glen Roy. Views of English Naturalists concerning Agassiz's Glacial Theory. Letter from Humboldt. Winter Visit to Glacier. Summer of 1841 on the Glacier. Descent into the Glacier. Ascent of the Jungfrau.