A few days before we left Pará, Senhor Pimenta Bueno invited his friends and acquaintances, who had expressed a wish to hear Mr. Agassiz’s views on the geological character of the Amazonian Valley, to meet at his house in the evening for that purpose. The guests were some two hundred in number, and the whole affair was very unceremonious, assuming rather the character of a meeting for conversation or discussion than that of an audience collected to hear a studied address. The substance of this talk or lecture, as subsequently written out by Mr. Agassiz, afterward appeared in the Atlantic Monthly, and is inserted here, with some few alterations under the head of a separate chapter. The reader will find occasional repetitions of facts already stated in the earlier part of the narrative; but they are retained for the sake of giving a complete and consistent review of the subject at this point of our journey, where it became possible to compare the geological structure of the Amazonian Valley with that of the southern provinces of Brazil and of those bordering on the Atlantic coast. * * * * * The existence of a glacial period, however much derided when first announced, is now a recognized fact. The divergence of opinion respecting it is limited to a question of extent; and after my recent journey in the Amazons, I am led to add a new chapter to the strange history of glacial phenomena, taken from the southern hemisphere, and even from the tropics themselves. I am prepared to find that the statement of this new phase of the glacial period will awaken among my scientific colleagues an opposition even more violent than that by which the first announcement of my views on this subject was met. I am, however, willing to bide my time; feeling sure that, as the theory of the ancient extension of glaciers in Europe has gradually come to be accepted by geologists, so will the existence of like phenomena, both in North and South America, during the same epoch, be recognized sooner or later as part of a great series of physical events extending over the whole globe. Indeed, when the ice-period is fully understood, it will be seen that the absurdity lies in supposing that climatic conditions so different could be limited to a small portion of the world’s surface. If the geological winter existed at all, it must have been cosmic; and it is quite as rational to look for its traces in the Western as in the Eastern hemisphere, to the south of the equator as to the north of it. Impressed by this wider view of the subject, confirmed by a number of unpublished investigations which I have made during the last three or four years in the United States, I came to South America, expecting to find in the tropical regions new evidences of a bygone glacial period, though, of course, under different aspects. Such a result seemed to me the logical sequence of what I had already observed in Europe and in North America.