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signs of stratification. 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.

The Valley of the Amazons was first sketched out by the elevation of two tracts of land; namely, the plateau of Guiana or the north, and the central plateau of Brazil on the south. It is probable that, at the time these two table-lands were lifted above the sea-level, the Andes did not exist, and the ocean flowed between them through an open strait.

Major Coutinho has found palæozoic deposits, with characteristic shells, in the valley of the Rio Tapajos, at the first cascade, and carboniferous deposits have been noticed along the Rio Guapore and the Rio Mamore. But the first chapter in the valley's geological history about which we have connected and trustworthy data is that of the cretaceous period. It seems certain, that, at the close of the secondary age, the whole Amazonian basin became lined with a cretaceous deposit, the margins of which crop out at various localities on its borders. 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 prov

It would seem (and this is a curious re-ince of Ceara. These fossil fishes were sult of modern geological investigations) that the portions of the earth's surface earliest raised above the ocean have trended from east to west. The first tract of land lifted above the waters in North America was also a long continental island, running from Newfoundland almost to the present base of the Rocky Mountains. This tendency may be attributed to various causes, to the rotation of the earth, the consequent depression of its poles, and the breaking of its crust along the lines of greatest tension thus produced. At a later period, the upheaval of the Andes took place, closing the western side of this strait, and thus transforming it into a gulf, open only toward the east. Little or nothing is known of the earlier stratified deposits resting against the crystal Eine masses first uplifted in the Amazonian Valley. There is here no sequence, as in North America, of Azoic, Silurian, Devonian, and Carboniferous formations, shored up against each other by the gradual upheaval of the continent, although unquestionably older palæozoic and secondary beds underlie, here and there, the later formations. Indeed,

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. In this connection, let me say that here and elsewhere I shall speak of the provinces of Ceara, Piauhy, and Maranham as belonging geologically to the Valley of the Amazons, though their shore is bathed by the ocean, and their rivers empty directly into the Atlantic. But I entertain no doubt, and I hope I may hereafter be able to show, that, at an earlier period, the northeastern coast of Brazil stretched much farther seaward than in our day; so far, indeed, that in those times the rivers of all these provinces must have been tributaries of the Amazon in its eastward course. The evidence for this conclusion is substantially derived from the identity of the deposits in the valleys belonging to these provinces with those of the valleys through which the actual tributaries of the Amazons flow; as, for instance, the Tocantins, the Xingu, the Tapajos, the Madura, etc. Besides the fossils above alluded to from the eastern borders of this an

cient basin, I have had recently another evidence of its cretaceous character from its southern region. Mr. William Chandless, on his return from a late journey on the Rio Purus, presented me with a series of fossil remains of the highest interest, and undoubtedly belonging to the cretaceous period. They were collected by himself on the Rio Aquiry, an affluent of the Rio Purus. Most of them were found in place between the tenth and eleventh degrees of south latitude, and the sixty-seventh and sixty-ninth degrees of west longitude from Greenwich, in localities varying from 430 to 650 feet above the sealevel. There are among them remains of Mososaurus, and of fishes closely allied to those already represented by Faujas in his description of Maestricht, and characteristic, as is well known to geological students, of the most recent cretaceous period.

Thus in its main features the Valley of the Amazons, like that of the Mississippi, is a cretaceous basin. This resemblance suggests a further comparison between the twin continents of North and South America. Not only is their general form the same, but their framework as we may call it, that is, the lay of their great mountain-chains and of their table-lands, with the extensive intervening depressions, presents a striking similarity. Indeed, a zoologist, accustomed to trace a like structure under variously modified animal forms, cannot but have his homological studies recalled to his mind by the coincidence between certain physical features in the northern and southern parts of the Western hemisphere. And yet here, as throughout all nature, these correspondences are combined with a distinctness of individualization, which leaves its respective character not only to each continent as a whole, but also to the different regions cir<cumscribed within its borders. In both, however, the highest mountainchains, the Rocky Mountains and Coast Range with their wide intervening tableland in North America, and the chain of the Andes with its lesser plateaus in

South America, run along the western coast; both have a great eastern promontory,- Newfoundland in the northern continent, and Cape St. Roque in the southern ;-and though the resemblance between the inland elevations is perhaps less striking, yet the Canadian range, the White Mountains, and the Alleghanies may very fairly be compared to the table-lands of Guiana and Brazil, and the Serra do Mar. Similar correspondences may be traced among the river systems. The Amazons and the St. Lawrence, though so different in dimensions, remind us of each other by their trend and geographical position; and while the one is fed by the largest river system in the world, the other drains the most extensive lake surfaces known to exist in immediate contiguity. The Orinoco, with its bay, recalls Hudson's Bay and its many tributaries, and the Rio Magdalena may be said to be the South American Mackenzie; while the Rio de la Plata represents geographically our Mississippi, and the Paraguay recalls the Missouri. The Parana may be compared to the Ohio; the Pilcomayo, Vermejo, and Salado rivers, to the River Platte, the Arkansas, and the Red River in the United States; while the rivers farther south, emptying into the Gulf of Mexico, represent the rivers of Patagonia and the southern parts of the Argentine Republic. 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.

But while in geographical homolo gy the Amazons compare with the St. Lawrence, and the Mississippi with the Rio de la Plata, the Mississippi and the Amazons, as has been said, resemble each other in their local geological character. They have both received a substratum of cretaceous beds, above

which are accumulated their more recent deposits, so that, in their most prominent geological features, both may be considered as cretaceous basins, containing extensive deposits of a very recent age. 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. 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. It happened that the first three or four months of my journey, August, September, October, and November, were those when the waters are lowest, reaching their minimum in September and October, and beginning to rise again in November, so that I had an excellent opportunity in ascending the river to observe its geological structure. Throughout its whole length, three distinct geological formations may be traced, the two lower of which have followed in immediate succession, and are conformable with one another, while the third rests unconformably upon them, following all the inequalites of the greatly denudated surface presented by the second formation. Notwithstanding this seeming interruption in the sequence of these deposits,

the third, as we shall presently see, belongs to the same series, and was accumulated in the same basin. The lowest set of beds of the whole series is rarely visible, but it seems everywhere to consist of sandstone, or even of loose sands well stratified, the coarser materials lying invariably below, and the finer above. Upon this lower set of beds rests everywhere an extensive deposit of fine laminated clays, varying in thickness, but frequently dividing into layers as thin as a sheet of paper. In some localities they exhibit in patches an extraordinary variety of beautiful colors, - pink, orange, crimson, yellow, gray, blue, and also black and white. The Indians are very skilful in preparing paints from these colored clays, with which they ornament their pottery, and the bowls of various shapes and sizes made from the fruit of the Cuieira-tree. These clay deposits assume occasionally a peculiar appearance, and one which might mislead the observer as to their true nature. When their surface has been long exposed to the action of the atmosphere and to the heat of the burning sun, they look so much like clay slates of the oldest geological epochs, that, at first sight, I took them for primary slates, my attention being attracted to them by a regular cleavage as distinct as that of the most ancient clay slates. And yet at Tonantins, on the banks of the Solimoens, in a locality where their exposed surfaces had this primordial appearance, I found in these very beds a considerable amount of well-preserved leaves, the character of which proves their recent origin. These leaves do not even indicate as ancient a period as the Tertiaries, but resemble so closely the vegetation of to-day, that I have no doubt, when examined by competent authority, they will be identified with living plants. The presence of such an extensive clay formation, stretching over a surface of more than three thousand miles in length and about seven hundred in breadth, is not easily explained under any ordinary circum

stances. The fact that it is so thorough by laminated shows that, in the basin in which it was formed the waters must have been unusually quiet containing identical materials throughout, and that these materials must have been deposted over the whole bottom in the same way. It is usually separated from the superincumbent beds by a glazed crust of hard, compact sandstone, almost resembling a ferruginous quartzite. Upon this follow beds of sand and sandstone, varying in the regularity of their strata, reddish in color, often highly ferruginous, and more or less nodulous or porous. They present frequent traces of cross-stratification, alternating with regularly stratified horizontal beds, with here and there an intervening layer of clay. It would seem as if the character of the water basin had now changed, and as if the waters under which this second formation was cposited had vibrated between storm and calm, — had sometimes flowed more gently, and again had been tossed to and fro,-giving to some of the beds the aspect of true torrential deposits. Indeed, these sandstone formations present a great variety of aspects. Sometimes they are very regularly laminated, or assume even the appearance of the hardest quartzite. This is usually the case with the uppermost beds. 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. This resemblance has, no doubt, led to the identification of the Amazonian deposits with the more ancient formations of Europe. At Monte Alegre, of which I shall presently speak more in detail, such a clay bed divides the lower from the upper sandstone. The

thickness of these sandstones is extremely variable. In the basin of the Amazons proper, they hardly rise anywhere above the level of high water during the rainy season, while at low water, in the summer months, they may be seen everywhere along the riverbanks. It will be seen, however, that the limit between high and low water gives no true measure of the original thickness of the whole series.

In the neighborhood of Almeirim, at a short distance from the northern bank of the river, and nearly parallel with its course, there rises a line of low hills, interrupted here and there, but extending in evident connection from Almeirim through the region of Monte Alegre to the heights of Obides. These hills have attracted the attention of travellers, not only from their height, which appears greater than it is, because they rise abruptly from an extensive plain, but also on account of their curious form, many of them being perfectly level on top, like smooth tables, and very abruptly divided from each other by low, intervening spaces. Nothing has hitherto been known of the geological structure of these hills, but they have been usually represented as the southernmost spurs of the table - land of Guiana. On ascending the river, I felt the greatest curiosity to examine them; but at the time I was deeply engrossed in studying the distribution of fishes in the Amazonian waters, and in making large ichthyological collections, for which it was very important not to miss the season of low water, when the fishes are most easily obtained. I was, therefore, obliged to leave this most interesting geological problem, and content myself with examining the structure of the valley so far as it could be seen on the riverbanks and in the neighborhood of my different collecting stations. On my return, however, when my collections were completed, I was free to pursue

*The atlas in Martins's "Journey to Brazil," or the sketch accompanying Bates's description of these hills in his "Naturalist on the Amazons," will give an idea of their aspect.

this investigation, in which Major Coutinho was as much interested as myself. We determined to select Monte Alegre as the centre of our exploration, the serra in that region being higher than elsewhere. As I was detained by indisposition at Manaos, for some days, at the time we had appointed for the excursion, Major Coutinho preceded me, and had already made one trip to the serra, with some very interesting results, when I joined him, and we made a second journey together.

Monte Alegre lies on a side arm of the Amazons, a little off from its main course. This side arm, called the Rio Gurupatuba, is simply a channel running parallel with the Amazons, and cutting through from a higher to a lower point. Its dimensions are, however, greatly exaggerated in all the maps thus far published, where it is usually made to appear as a considerable northern tributary of the Amazons. The town stands on an elevated terrace, separated from the main stream by the Rio Gurupatuba, and by an extensive flat, consisting of numerous lakes divided from each other by low alluvial land, and mostly connected by narrow channels. To the west of the town, this terrace sinks abruptly to a wide sandy plain called the Campos, covered with a low forest growth, and bordered on its farther limit by the picturesque serra of Erreré. The form of this mountain is so abrupt, its rise from the plain so bold and sudden, that it seems more than twice its real height. Judging by the eye, and comparing it with the mountains I had last seen, the Corcovado, the Gavia and Tijuca range in the neighborhood of Rio, I had supposed it to be three or four thousand feet high, and was greatly astonished when our barometric observations showed it to be somewhat less than nine hundred feet in its most elevated point. This, however, agrees with Martins's measurement of the Almeirim hills, which he says are eight hundred feet in height.

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. As this was almost the only occasion in all my journey when I passed a day in the pure enjoyment of nature, without the labor of collecting, which in this hot climate, where specimens require such immediate and constant attention, is very great, I am tempted to interrupt our geology for a moment, to give an account of it. 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; for under such circumstances all things are seen in their true relations. Unhappily, it is not easy to present the picture as a whole, for all our written descriptions are more or less dependent on nomenclature, and the local names are hardly known out of the districts where they belong, while systematic names are familiar to few.

I started before daylight; but, as the dawn began to redden the sky, large flocks of ducks, and of the small Amazonian geese, might be seen flying towards the lakes. Here and there a cormorant sat alone on the branch of a dead tree, or a kingfisher poised himself over the water, watching for his prey. Numerous gulls were gathered in large companies on the trees along the river-shore; alligators lay on its surface, diving with a sudden plash at the approach of our canoe; and occasionally a porpoise emerged from the water, showing himself for a moment

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