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The Amazon River, geology. - The Amazon River, in the region where we camped and, in all its extension, is accompanied by one of the main orogeny (gold-producing) formations: that of grain. It is divided into two formations, which in the narrative part of the trip referring to Minas Gerais and Piauí we have already mentioned with the name of grains of stone, and the one to which the new geologists gave the name of cupric grains.

Examination of the geognostatic conditions of this basin is particularly difficult in territory covered with virgin forest, which, to an immeasurable extent, does not rise to a mountain, let alone a hill, and only rarely lets the living rock emerge; it rarely appears under a thick layer of sand, damp or red clay in the cuts made by rivers and streams.

No mining is exploited throughout the State of Grande Para; well, it is not necessary to open them anywhere, given the great influx of springs and other waters and the Mosqueiro quarry in Belem do Para, is the only one now explored in Escacio because the interior constructions are made only of clay, framework and mud. As finally, all trips in this province are made only by water, so it follows that on dry land, little sought after, the orogenic constitution can only be examined under very narrow circumstances.

Grain formation also occurs in this northernmost region of Brazil under three major forms, that is, as rusty grains, often combining with the loophole mode; as grains of very fine granulation, generally colder and redder; or, thirdly, as harder and whiter grains.

The first of these forms, which we found ourselves, both in the province of Maranhao, along the shores of Itapicuru, to the sea, and on the island of Maranhao. occurs in Para and Amazonas, to a great extent.

We find it outcropping on the outskirts of Belem do Para, on the southwestern part of Marajo Island, in Gurupa: and Almeirim;

Tabular mountain

it forms also the tabular mountains of Para, which, completely isolated from the group of the mountains of Parime, run along the northern bank of the Amazon, ending in the west with the grass-covered hill of Monte Alegre, descending, however, to the east to the sands of Macapa. The same formation occurs, almost without interruption, also at Barreiros de Cuzari, on the rather high banks of the Tapajos, at Santarem, on Paricatuba Island,

Paricatuba

lined with close cacao trees,

and at the palm-lined banks of the Iraria Canal;

Etching 41

but beyond, to the west, this stone is constantly interrupted by other formations: it alternates with deposits of mottled loam, clay, a whitish limestone or the second major form of red grains, which occurs particularly west of the Jatauarana Rapids

in the the banks of Matari and Puraque Cuara to the Rio Negro, then continue along the banks of this last river to its border point to Airao, and travels far along the Solimoes to where we sailed it, sometimes along the steep banks, then farther inland. It has white grains of fine granulation, very crystalline and hard, which, besides, does not present, by any state, as belonging to another formation, and we found it outcropping near Canoma. Therefore, these various modifications of grain in the Amazon Basin immediately join that of the lower Japuri basin.

The orictognostic presentations of the rust grain of breach are the most varied.

Rust grain ?

The ferrous clayey layer alternates in violet, brown, red and yellow colors: the quartz pebbles, or mortar conglomerates, appear, sometimes very beautiful and crystalline,

Pink quartz pebbles

sometimes rolled and noticeable contours to the size of a hazelnut. The stone is sometimes very compact, and, by its hardness, suitable for construction, sometimes containing finely crumbling clay, sometimes hard inclusions in the clay or larger conglomerates of a very common stone, which give rise to the assumption that the mountain itself had passed through partial regeneration. The second and third forms of this orogeny (gold production), red (keuprica) and white gres (stone) appear in a few varieties, each differing only according to the coarser or finer granulation, and the color, most commonly red pale flesh; sometimes, however, it is also light purple, gray-brown, gray and white with many graduations.

In this orogeny, stratification is very indistinctly observed. Ferritic grain conglomerate often occurs in large thickness, so smooth and flat, as a large yard. Now it lies just above the granite (Araraquara),

Araraquara waterfall

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