A narrative of travels on the Amazon and Rio Negro,

by Alfred Russel Wallace

F. Reeve, imp.

The extreme variation of the barometer at Pará for three years was only three-tenths of an inch (see diagram, [Plate IV.]). The mean height, with all the necessary corrections, would seem to be almost exactly thirty inches; I have however already given my reasons for believing that there is a considerable difference in the pressure of the atmosphere in the interior of the country. In the month of May some very cold days are said to occur annually on the Upper Amazon and Rio Negro; but I never experienced anything of the kind very remarkable myself. Many intelligent persons have assured me that they sometimes are so severe that the inhabitants suffer much, and, what is much more extraordinary, the fishes in the rivers die of it. Allowing this to be the fact, I am quite unable to account for it, as it is difficult to conceive that a diminution of temperature of five or ten degrees, which is as much as ever takes place, can produce any effect upon them.

I have an authentic account of hail having once fallen on the Upper Amazon, a remarkable occurrence at a place only three degrees south of the equator, and about two hundred feet above the level of the sea. The children were out at play, and brought it to their parents, astonished at a substance falling from the clouds quite new to them, and which was so remarkably cold. The person who told me was a Portuguese, and his information can be perfectly relied on.

CHAPTER XV.

VEGETATION OF THE AMAZON VALLEY.

Perhaps no country in the world contains such an amount of vegetable matter on its surface as the valley of the Amazon. Its entire extent, with the exception of some very small portions, is covered with one dense and lofty primeval forest, the most extensive and unbroken which exists upon the earth. It is the great feature of the country,—that which at once stamps it as a unique and peculiar region. It is not here as on the coasts of southern Brazil, or on the shores of the Pacific, where a few days’ journey suffices to carry us beyond the forest district, and into the parched plains and rocky serras of the interior. Here we may travel for weeks and months inland, in any direction, and find scarcely an acre of ground unoccupied by trees. It is far up in the interior, where the great mass of this mighty forest is found; not on the lower part of the river, near the coast, as is generally supposed.

A line from the mouth of the river Parnaíba, in long. 41° 30’ W., drawn due west towards Guayaquil, will cut the boundary of the great forest in long. 78° 30’, and, for the whole distance of about 2600 miles, will have passed through the centre of it, dividing it into two nearly equal portions.

For the first thousand miles, or as far as long. 56° W., the width of the forest from north to south is about four hundred miles; it then stretches out both to the north and south, so that in long. 67° W. it extends from 7° N., on the banks of the Orinooko, to 18° S., on the northern slope of the Andes of Bolivia, a distance of more than seventeen hundred miles. From a point about sixty miles south-east of Tabatinga, a circle may be drawn of 1100 miles in diameter, the whole area of which will be virgin forest.

Along the Andes of Quito, from Pasto to Guancabamba, it reaches close up to the eastern base of the mountains, and even ascends their lower slopes. In the moderately elevated country between the river Huallaga and Marañon, the forest extends only over the eastern portion, commencing in the neighbourhood of Moyobamba. Further on, to the east of Cuzco and La Paz, it spreads high up on the slopes of the Bolivian Andes, and passing a little to the west of Santa Cruz de la Sierra, turns off to the north-east, crossing the Tapajóz and Xingú rivers somewhere about the middle of their course, and the Tocantíns not far above its junction with the Araguáya, and then passes over to the river Parnaíba, which it follows to its mouth.