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the Orinoco and the Amazon, which themselves constitute a geographic singularity, are found in the great plains little inclined towards low mountains; isolated; with the anomalous formation of the junction channel, the Caciquiare, and of Rio Negro itself, in the form of a canal, and with a number of lakes, lagoons and rivers, which now communicate through channels, sometimes, close to their sources, very short distances and well passable that all meet in a rare geographic set.
    
 The large basin presents very simple geological conditions. Only these formations appear in the vast territory of stoneware and granite.

Granite

The former seems identical to that which predominates on Maranhao Island and, from Belem do Para onwards, generally in the Amazon basin,

Amazon Basin

and in Germany was designated with the new name of pecilito (gres keuprico). Its structure manifests itself in three main forms: as reddish sandstone,

with a very fine granulation; like sedimentary rock that is whiter, very hard, stratified; finally as reddish, brownish sandstone, containing a lot of iron,

yellowish or purplish, that transforms into ferruginous sedimentary rock.

The first formation, similar to what we observe in Barra do Rio Negro and Coari, seems to follow the river up to Maripi. Henceforth, there is hardly any brown sandstone, very ferruginous, in different cases containing earth, and transitioning to multicolored deposits of clay and loam, yellow, rosy red, and alternating with it. One does not perceive a certain orientation in this formation. This is repeated with many alternations in the granite, which I found covering the Serra de Araraquara, six to eight feet thick.

The clay deposits (marl) of this rock, in several places of the upper river basin (for example, above the mouth of the River of Enganos and in the Barrancos de Oacari), especially in the places where they rest on the living stone,

contain deposits of sulphate of very white iron, which easily disintegrates, sometimes in balls, sometimes in bunches, sometimes in cubic crystals heaped together.

Ferruginous sandstone

Sometimes a nucleus of iron sulphate is encased in a brown layer of ferruginous sandstone. The trunks of trees, buried in these marl deposits, are often crossed by the mass of iron sulphate; and in the fountains and streams from the high banks to the river many phenomena give the indication of the iron sulphate dissolved in them, which is lost in the ferruginous sandstone and in these trunks in the river bed. By itself this ferruginous sandstone is dissolved, and again makes a conglomerate with quartz breccia

Quartz breccia

and with yellow or red jasper,

Red Jasper

which I never found in its primitive deposit, constituting a breach that forms in the river, here and there, as banks and dams. It must be entirely identical to the formation of the Meriti-parana, where the crew also brought me iron sulphate

Iron sulfate

and marl of beautiful colors. Another formation of keupric sandstone is probably the white stoneware of fine granulation, which is very hard, and is found on Cupati's mountain, and perhaps also the mountain to the north of it, in Tiquie. The layers of this hard stoneware, alternating from a few inches to a yard, orient themselves in the second and third hours of the Freiberg compass from the northwest and southeast, and descend at a 20 ° to 50 ° angle to the east.

The formation of sandstone is much more extensive in the basin of the Japura than the simple granite. I have only found this last west of Riacho Jui, and it is stratified both in the river itself and in several points of the Araraquara mountain.

Araraquara waterfall

The granite, from which the river springs in Poco-acu, and from there to the west to the mouth of the River of Enganos, is of uncommon hardness, of fine granulation, of texture almost like the porphyry.

Granite formations

For this reason, the Indians living there make axes with it. But what forms the cliffs of Araraquara, is true primitive granite,

Primitive granite

and of more friable and coarse granulation. It consists of flesh-colored red feldspar, whitish quartz and large sheets of white, silver-colored mica. Stratification is not noticeable, but there are thin reddish granite filaments, which cross the main mass in one to two pound thickness, especially in the direction of north-south and north-west to south-east.

Mica-schist

Further westward, a formation of micaxist above the formation of granite is to be followed; at least, I found pebbles from the micaxist in the bed of Japura in Araraquara; and also at the mouth of the Apaporis, in which, according to the Indians, there is also a stone equal to that of Poco-acu, that is, granite.

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