Jean Louis Rodolphe Agassiz

“ Through such a forest, where the animal life was no less rich and varied than the vegetation, our boat glided slowly for hours. The number and variety of birds struck me with astonishment. The coarse sedgy grasses on either side were full of water birds, one of the most common of which was a small chestnut-brown wading bird, the Jaçana (Parra) , whose toes are immensely long in proportion to its size, enabling it to run upon the surface of the aquatic vegetation, as if it were solid ground. ”

“ Of the history of the Amazonian Valley during the periods immediately following the Cretaceous, we know little or nothing. Whether the Tertiary deposits are hidden under the more modern ones, or whether they are wholly wanting, the basin having, perhaps, been raised above the sea-level before that time, or whether they have been swept away by the tremendous inundations in the valley, which have certainly destroyed a great part of the cretaceous deposit, they have never been observed in any part of the Amazonian basin. ”

“ But while the features to which I have 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. ”

“ Indeed, in all regions, however far away from his own home, in the midst of a fauna and flora entirely new to him, the traveller is startled occasionally by the song of a bird or the sight of a flower so familiar that it transports him at once to woods where every tree is like a friend to him. ”

“ 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 southward 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. ”

“ 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. ”

“ The fact that these were accumulated in a glacial basin would, indeed, at once account for the traces of vegetable life, and for the absence, or at least the great scarcity, of animal remains in these deposits. For while fruits may ripen and flowers bloom on the very edge of the glaciers, it is also well known that the fresh-water lakes formed by the melting of the ice are singularly deficient in life. There are indeed hardly any animals to be found in glacial lakes. ”

“ It is reversing the natural order of things to give results without the investigations which have led to them; and I should not have introduced the subject here except to show that the fresh-water denudations and the oceanic encroachments which have formed the Amazonian Valley, with its river system, are not isolated facts, but that the process has been the same in both continents. The extraordinary continuity and uniformity of the Amazonian deposits are due to the immense size of the basin enclosed, and the identity of the materials contained in it. ”

“ No doubt the fertility arises from the great variety of chemical elements contained in the drift, and the kneading process it has undergone beneath the gigantic ice-plough,—a process which makes glacial drift everywhere the most fertile soil. Since my return from the Amazons, my impression as to the general distribution of these phenomena has been confirmed by the reports of some of my assistants, who have been travelling in other parts of the country. ”

“ The ocean has gradually eaten its way into this deposit, and given its present outlines to the continent. These denudations of the sea no doubt began as soon as the breaking up of the ice exposed the drift to its invasion; in other words, at a time when colossal glaciers still poured forth their load of ice into the Atlantic, and fleets of icebergs, far larger and more numerous than those now floated off from the Arctic seas, were launched from the northeastern shore of the United States. Many such masses must have stranded along the shore, and have left various signs of their presence. ”

“ 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.
I have spoken of Tijuca and the Dom Pedro Railroad as favorable localities for studying the peculiar southern drift; but one meets it in every direction. A sheet of drift, consisting of the same homogeneous, unstratified paste, and containing loose materials of all sorts and sizes, covers the country. ”

“ No seashells nor remains of any marine animal have as yet been found throughout their whole extent, over a region several thousand miles in length and from five to seven hundred miles in width. It is contrary to all our knowledge of geological deposits to suppose that an ocean basin of this size, which must have been submerged during an immensely long period in order to accumulate formations of such a thickness, should not contain numerous remains of the animals formerly inhabiting it. ”

“ 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. ”

“ I learned how rich a single day may be in this wonderful tropical world, if one's eyes are only open to the wealth of animal and vegetable life. Indeed, a few hours so spent in the field, in simply watching animals and plants, teaches more of the distribution of life than a month of closet study ”

“ It is also everywhere underlaid by coarse, well-stratified deposits, resembling somewhat the recife of Bahia and Pernambuco; whereas the unstratified drift of the south rests immediately upon the undulating surface of whatever rock happens to make the foundation of the country, whether stratified or crystalline. The peculiar sandstone on which the Amazonian clay rests exists nowhere else. Before proceeding, however, to describe the Amazonian deposits in detail, I ought to say something of the nature and origin of the valley itself. ”

“ Much of the river-shore consisted of low alluvial land, and was covered with that peculiar and beautiful grass known as Capim; this grass makes an excellent pasturage for cattle, and the abundance of it in this region renders the district of Monte Alegre very favorable for agricultural purposes. Here and there, where the red clay soil rose above the level of the water, a palm-thatched cabin stood on the low bluff, with a few trees about it. ”

“ 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 ”

“ Whatever tertiary deposits are represented in geological maps of this region are so marked in consequence of an incorrect identification of strata belonging, in fact, to a much more recent period.
A minute and extensive survey of the Valley of the Amazons is by no means an easy task, and its difficulty is greatly increased by the fact that the lower formations are only accessible on the river margins during the vasante, as it is called, or dry season, when the waters shrink in their beds, leaving a great part of their banks exposed. ”

“ This is shown by the fact that in this ochre-colored clay, and penetrating to a greater or less depth the sandstone below, are dug, not only the great longitudinal channel of the Amazons itself, but also the lateral furrows through which its tributaries reach the main stream, and the network of anastomosing branches flowing between them; the whole forming the most extraordinary river system in the world. ”

“ 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. ”

“ Major Coutinho and I reached the serra by different roads; he crossing the Campos on horseback with Captain Faria, the commander of our steamer, and one or two other friends from Monte Alegre, who joined our party, while I went by canoe. The canoe journey is somewhat longer. A two hours' ride across the Campos brings you to the foot of the mountain, whereas the trip by boat takes more than twice that time. But I preferred going by water, as it gave me an opportunity of seeing the vast variety of animals haunting the river-banks and lakes. ”

“ After the waters had been drained off from the more elevated ridges, these depressions would still remain full. In the lakes and pools thus formed, stratified deposits would be accumulated, consisting of the most minutely comminuted clay, deposited in thin laminated layers, or sometimes in considerable masses, without any sign of stratification; such differences in the formation being determined by the state of the water, whether perfectly stagnant or more or less agitated. Of such pool deposits overlying the drift there are many instances in the Northern United States. ”

“ 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. ”

“ In other localities, and more especially in the lowermost beds, the whole mass is honeycombed, as if drilled by worms or boring shells, the hard parts enclosing softer sands or clays. Occasionally the ferruginous materials prevail to such an extent, that some of these beds might be mistaken for bog ore, while others contain a large amount of clay, more regularly stratified, and alternating with strata of sandstone, thus recalling the most characteristic forms of the Old Red or Triassic formations. ”

“ The thickness of the deposits gives a measure for the colossal scale of the denudations by which this immense accumulation was reduced to its present level. Here then is a system of high hills, having the prominence of mountains in the landscape, produced by causes to whose agency inequalities on the earth's surface of this magnitude have never yet been ascribed. We may fairly call them denudation mountains. ”

“ My investigation of the island itself, in connection with the coast and the river, leads me to suppose that, having been at one time an integral part of the deposits described above, at a later period it became an island in the bed of the Amazons, which, dividing in two arms, encircled it completely, and then, joining again to form a single stream, flowed onward to the sea-shore, which in those days lay much farther to the eastward than it now does. ”

“ They have been observed along its southern limits, on its western outskirts along the Andes, in Venezuela along the shore-line of mountains, and also in certain localities near its eastern edge. I well remember that one of the first things which awakened my interest in the geology of the Amazonian Valley was the sight of some cretaceous fossil fishes from the province of Ceara. These fossil fishes were collected by Mr. George Gardner, to whom science is indebted for the most extensive information yet obtained respecting the geology of that part of Brazil. ”

“ Not only is there this general correspondence between the mountain elevations and the river systems, but as the larger river basins of North America—those of the St. Lawrence, the Mississippi, and the Mackenzie—meet in the low tracts extending along the foot of the Rocky Mountains, so do the basins of the Amazons, the Rio de la Plata, and the Orinoco join each other along the eastern slope of the Andes. ”