PHYSICAL HISTORY OF THE VALLEY OF THE AMAZONS. I. YEAR or two ago I published in On my arrival in Rio de Janeiro, — A the Atlantic Monthly, as part of the port at which I first landed in Bra 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 Impressed by this wider view of the subject, confirmed by a number of unpublished investigations which I have made during the last three or four years in the United States, I came to South America, expecting to find in the tropical regions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 Europe and in North America. VOL. XVIIL-NO. 105. 4 zil, 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 of any one familiar with similar facts observed in other parts of the world, that this is one of the many forms of drift connected with glacial action. I was, however, far from anticipating, when I first met it in the neighborhood of Rio, that I should afterwards find it spreading over the surface of the country, from north to south and from east to west, with a continuity which gives legible connection to the whole geological history of the continent. It is true that the extensive decomposition of the underlying rock, penetrating sometimes to a considerable depth, makes it often difficult to distinguish between it and the drift; and the problem is made still more puzzling by the fact that the surface of the drift, when baked by exposure to the hot sun, often assumes the appearance of decomposed rock, so that great care is required for a correct interpretation of the facts. A little practice, however, trains the eye to read these appearances aright, and I may say that I have learned to recognize everywhere the limit between the two formations. There is indeed one safe guide, namely, the undulating line, reminding one of roches moutonnées,* and marking the irregular surface of the rock on which the drift was accumulated; whatever modifications the one or the other may have undergone, this line seems never to disappear. Another deceptive feature, arising from the frequent disintegration of the rocks and from the brittle character of some of them, is the presence of loose fragments, which simulate erratic boulders, but are in fact only detached masses of the rock in place. A careful examination of their structure, however, will at once show the geologist whether they belong where they are found, or have been brought from a distance to their present resting-place. But while the features to which I have * The name consecrated by De Saussure to designate certain rocks in Switzerland, which have had their surfaces rounded under the action of the glaciers. Their gently swelling outlines are thought to resemble sheep resting on the ground, and for this reason the people in the Alps call them roches moutonnées. alluded are unquestionably drift phenomena, they present in their wider extension, and especially in the northern part of Brazil, as will hereafter be seen, some phases of glacial action hitherto unobserved. Just as the investigation of the ice period in the United States has shown us that ice-fields may move over open level plains, as well as along the slopes of mountain valleys, so does a study of the same class of facts in South America reveal new and unlooked-for features in the history of the ice period. Some will say, that the fact of the advance of ice-fields over an open country is by no means established, inasmuch as many geologists believe all the so-called glacial traces, viz. striæ, furrows, polish, etc., found in the United States, to have been made by floating icebergs at a time when the continent was submerged. To this I can only answer, that in the State of Maine I have followed, compass in hand, the same set of furrows, running from north to south in one unvarying line, over a surface of one hundred and thirty miles from the Katahdin Iron Range to the sea-shore. These furrows follow all the inequalities of the country, ascending ranges of hills varying from twelve to fifteen hundred feet in height, and descending into the intervening valleys only two or three hundred feet above the sea, or sometimes even on a level with it. I take it to be impossible that a floating mass of ice should travel onward in one rectilinear direction, turning neither to the right nor to the left, for such a distance. Equally impossible would it be for a detached mass of ice, swimming on the surface of the water, or even with its base sunk considerably below it, to furrow in a straight line the summits and sides of the hills, and the beds of the valleys. It would be carried over the depressions without touching bottom. Instead of ascending the mountains, it would remain stranded against any elevation which rose greatly above its own basis, and, if caught between two parallel ridges, would float up and down between them. Moreover, the action of solid, unbroken ice, moving over the ground in immediate contact with it, is so different from that of floating icerafts or icebergs, that, though the latter have unquestionably dropped erratic boulders, and made furrows and striæ on the surface where they happened to be grounded, these phenomena will easily be distinguished from the more connected traces of glaciers, or extensive sheets of ice, resting directly upon the face of the country and advancing over it. There seems thus far to be an inextricable confusion, in the ideas of many geologists, as to the respective action of currents, icebergs, and glaciers. It is time they should learn to distinguish between classes of facts so different from each other, and so easily recognized after the discrimination has once been made. As to the south ward movement of an immense field of ice, extending over the whole north, It seems inevitable, the moment we admit that snow may accumulate around the pole in such quantities as to initiate a pressure radiating in every direction. Snow, alternately thawing and freezing, must, like water, find its level at last. A sheet of snow ten or fifteen thousand feet in thickness, extending all over the northern and southern portions of the globe, must necessarily lead, in the end, to the formation of a northern and southern cap of ice, moving toward the equator. abrupt ascents; as, for instance, on the Corcovado, along the path leading up the mountain, are some very fine banks of drift, the more striking from the contrast of their deep red color with the surrounding vegetation. I have myself followed this sheet of drift from Rio de Janeiro to the top of the Serra do Mar, where, just outside the pretty town of Petropolis, the river Piabanha may be seen flowing between banks of drift, in which it has excavated its bed; thence I have traced it along the beautiful macadamized road leading to Juiz de Fora in the province of Minas Geraes, and beyond this to the farther side of the Serra da Babylonia. Throughout this whole tract of country, in the greater part of which travelling is easy and delightful, -an admirable line of diligences, over one of the finest roads in the world, being established as far as Juiz de Fora, — the drift may be seen along the roadside, in immediate contact with the native crystalline rock. The fertility of the land, also, is a guide to the presence of drift. Wherever it lies thickest over the surface, there are the most flourishing coffee-plantations; and I believe that a more systematic regard to this fact would have a most beneficial influence upon the agricultural interests of the country. No doubt the fertility arises from the great variety of chemical elements contained in the drift, and the kneading process it has undergone beI have spoken of Tijuca and the Dom neath the gigantic ice-plough, · a proPedro Railroad as favorable localities cess which makes glacial drift everyfor studying the peculiar southern drift; where the most fertile soil. Since my but one meets it in every direction. A return from the Amazons, my impression sheet of drift, consisting of the same as to the general distribution of these homogeneous, un stratified paste, and phenomena has been confirmed by the containing loose materials of all sorts reports of some of my assistants, who and sizes, covers the country. It is have been travelling in other parts of of very uneven thickness, - sometimes the country. Mr. Frederick C. Hartt, acthrown into relief, as it were, by the sur- companied by Mr. Copeland, one of the rounding denudations, and rising into volunteer aids of the expedition, has bills, sometimes reduced to a thin been making collections and geological layer, sometimes, as, for instance, on observations in the province of Spiritu steep slopes, washed entirely away, Santo, in the valley of the Rio Doce, leaving the bare face of the rock ex- and afterwards in the valley of the Muposed. It has, however, remained com- cury. He informs me that he has paratively undisturbed on some very found everywhere the same sheet of red, unstratified clay, with pebbles and occasional boulders, overlying the rock in place. Mr. Orestes St. John, who, taking the road through the interior, has visited, with the same objects in view, the valleys of the Rio San Francisco and the Rio das Velhas, and also the valley of Piauhy, gives the same account, with the exception that he found no erratic boulders in these more northern regions. The rarity of erratic boulders, not only in the deposits of the Amazons proper, but in those of the whole region which may be considered as the Amazonian basin, is accounted for, as we shall see hereafter, by the mode of their formation. The observations of Mr. Hartt and Mr. St. John are the more valuable, because I had employed them both, on our first arrival in Rio, in making geological surveys of different sections on the Dom Pedro Railroad, so that they had a great familiarity with those formations before starting on their separate journeys. Recently, Mr. St. John and myself having met at Pará on returning from our respective journeys, I have had an opportunity of comparing on the spot his geological sections from the valley of the Piauhy with the Amazonian deposits. There can be no doubt of the absolute identity of the formations in these valleys. Having arranged the work of my assistants, and sent several of them to collect and make geological examinations in other directions, I myself, with the rest of my companions, proceeded up the coast to Pará. I was surprised to find at every step of my progress the same geological phenomena which had met me at Rio. As the steamer stops for a number of hours, or sometimes for a day or two, at Bahia, Maceio, Pernambuco, Parahiba, Natal, Ceara, and Maranham, I had many opportunities for observation. It was my friend Major Coutinho, already an experienced Amazonian traveller, who first told me that this formation continued through the whole valley of the Amazons, and was also to be found on all of its affluents which he had vis ited, although he had never thought of referring it to so recent a period. And here let me interrupt the course of my remarks to say, that the facts recorded in this article are by no means exclusively the result of my own investigations. They are in great part due to this able and intelligent young Brazilian, a member of the government corps of engineers, who, by the kindness of the Emperor, was associated with me in my Amazonian expedition. I can truly say that he has been my good genius throughout the whole journey, saving me, by his previous knowledge of the ground, from the futile and misdirected expenditure of means and time often inevitable in a new country, where one is imperfectly acquainted both with the people and their language. We have worked together in this investigation; my only advantage over him being my greater familiarity with like phenomena in Europe and North America, and consequent readiness in the practical handling of the facts, and in perceiving their connection. Major Coutinho's assertion, that on the banks of the Amazons I should find the same red, unstratified clay as in Rio and along the southern coast, seemed to me at first almost incredible, impressed as I was with the generally received notions as to the ancient character of the Amazonian deposits, referred by Humboldt to the Devonian, and by Martins to the Triassic period, and considered by all travellers to be at least as old as the Tertiaries. The result, however, confirmed his report, at least so far as the component materials of the formation are concerned; but, as will be seen hereafter, the mode of their deposition, and the time at which it took place, have not been the same at the north and south; and this difference of circumstances has modified the aspect of a formation essentially the same throughout. At first sight, it would indeed appear that this formation, as it exists in the valley of the Amazons, is identical with that of Rio; but it differs from it in the rarity of its boulders, and in showing occasional |