PHYSICAL HISTORY OF THE VALLEY OF THE AMAZONS.
I.
A year or two ago I published in the Atlantic Monthly, as part of a series of geological sketches, a number of articles on the glacial phenomena of the Northern hemisphere. To-day I am led to add a new chapter to that strange history, 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 intense 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 Impressed by this wider view of the subject, confirmed by a number of unpublished investigations which I have made during the last three or four years in the United States, I came to South America, expecting to find in the tropical regions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 by-gone 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.
On my arrival in Rio de Janeiro,—the port at which I first landed in Brazil,—my attention was immediately attracted by a very peculiar formation, consisting of an ochraceous, highly ferruginous sandy clay. During a stay of three months in Rio, whence I made many excursions into the neighboring country, I had opportunities of studying this deposit, both in the province of Rio de Janeiro and in the adjoining province of Minas Geraes. I found that it rested everywhere upon the undulating surfaces of the solid rocks in place, was almost entirely destitute of stratification, and contained a variety of pebbles and boulders. The pebbles were chiefly quartz, sometimes scattered indiscriminately throughout the deposit, sometimes lying in a seam between it and the rock below; while the boulders were either sunk in its mass or resting loose on the surface. At Tijuca, a few miles out of the city of Rio, among the picturesque hills lying to the southwest of it, these phenomena may be seen in great perfection. Near Bennett's Hotel—a favorite resort, not only with the citizens of Rio, but with all sojourners there who care to leave the town occasionally for its beautiful environs—may be seen a great number of erratic boulders, having no connection whatever with the rock in place, and also a bluff of this superficial deposit studded with boulders, resting above the partially stratified metamorphic rock. Other excellent opportunities for observing this formation, also within easy reach from the city, are afforded along the whole line of the Railroad of Dom Pedro Segundo, where the cuts expose admirable sections, showing the red, unstratified, homogeneous mass of sandy clay resting above the solid rock, and often divided from it by a thin bed of pebbles. There can be no doubt, in the mind
