Remember the Rainforest 1
as in Japura, sometimes it covers the reddish grain, sometimes alternates with it, but in smaller masses. In Paricatuba, and near Obidos, it runs a very fine grained gneiss,
somewhat calcareous, and very hard, reddish quartz.
As for secondary deposits, there are in this mountain formations so widely scattered, we found only those of marl, of colored clay in porcelain earth, often outcropping along the river; and in Taguba Cuara, in Tapajos, those of iron sulphate and plaster.
Colored clay deposits, sometimes occurring to a great extent along the river, are the only variant that gives the monotony of this orogenic formation a pleasant diversion.
If the water of the river is in the ebb and the banks of different shades appear, already from far away attract the eye of the traveler by the colors white, yellow, red and violet, with which they stand out from the mirror of the water. The village of Serpa was named after the Indians as lta-coatiara, that is, "painted stone," because of these clay banks. The marginal red ravines are given the denomination, Cuara-piranga, "red place"; yellow, taud; to white, taua (Tabatinga) properly "yellowish white". These colorful clays, often very thin and friable, are the ones they continually use for their body paintings.
The filamentous and compact plaster brought to us from Taguba Cuara is entirely identical to Keupric stone; but the deposit is above a limestone formation that I myself have never seen anywhere in the Amazon. Also the most recent deposits of pyrite sulfite
which, impregnated with iron sulfate,
makes the transition to lignite and tree trunks, identical to those found in the Upper Japura marl, did not appear to us here. As a more recent formation, there are also sometimes, as in Obidos, deposits of a large gray grain, pink or white, of poor cohesion, whose alloy is limestone; elsewhere, there is a very recent breach of rust quartz gres
and jasper, in rough, angular, and conglomerate pieces.
These are the extremely simple geognostic conditions we had the opportunity to watch in the Amazon River Basin. They only become interesting when it is possible to harmonize them with neighboring orogenic formations. But if one takes a look at the adjacent territories on the south side, there is no doubt, as it were, that the predominant formation in the province of Piaui is also a reddish grain, rising to tabular mountains,
now covered with grasses. greyish green, now of palm-lined marshes and undergrowth, and to the east side covered with rust, gravel, is Itapicuru and the Maranhao province; but to the north the keupric (reddish) grain of the Amazon is repeated.
Serra de Ibiapaba
The dense forest-covered granite Serra de Ibiapaba - the third chain, "from the east, which runs in part from the coast along the mainland of Brazil, while forming the southwestern border of Piaui, - It also divides the two territories, by climate, natural products and different characteristics.The territory to the north of it belongs to the great Amazon Basin.
By the throat of the Dois Irmaos, we had passed a few miles north over it, finding, beyond a limestone of transition, which emerges in Pocoes de Cima, deposited on the gneiss and nothing more than the same formation of keupric grains were upon it. On this same stone we walked through palm trees and marshy fields to the Itapicuru River.
In the Turi River, gold mines were discovered, in the year 1818, on whose formation nothing positive could be proposed; but a few pieces taken from there, which show the pure metal in a milky white or gray quartz,
do not justify the possibility of the same formation occurring here as well. In Minas Gerais, a large iron ore stratum appears, sometimes filling the valleys, sometimes covering, like a cape, the summits of the highest mountains, and almost everywhere containing gold.
This orogeny (gold-producing), which is called there in the Tupic language, tapanacanga "head of black", and the conglomerate of iron grains, is almost always absolutely similar to that of the Amazon Basin; However, the latter lacks both gold,
whose fractures appear incorporated in many cases. This equality of formation, in such a vast territorial space, deserves great attention, because there has been