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Page:Popular Science Monthly Volume 38.djvu/222

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land. The silent story of the uprooted trees that lie matted and tangled and twisted together upon the shore, sometimes half buried in the sand, as if they were nothing more than so many strings or bits of paper, is deeply impressive. Forests so dense that I do not know how to convey an adequate idea of their density and gloom, are uprooted, torn, and swept away like chaff; and, after the full force of the waves is broken, they sweep on inland, leaving the débris with which they were loaded heaped and strewn through the forests, or lodged in the very tree-tops. The most powerful roots of the largest trees can not withstand the pororóca, for the ground itself is torn up to great depths in many places, and carried away by the flood to make bars, add to old islands, or build up new ones. Before seeing these evidences of its devastation, I had heard what I considered very extravagant stories of the destructive power of the pororóca; but, after seeing them, doubt was no longer possible. The lower or northern ends of the islands of Bailique and Porquinhos seemed to feel the force of the waves at the time of my visit more than any of the other islands on the southeast side of the river, while on the northern side the forest was wrecked and the banks washed out far above Ilha Nova.

The explanation of this phenomenon, as given by Condamine, appears to be the correct one—that is, that it is due to the incoming tide meeting resistance in the form of immense sand-bars in some places and narrow channels in others. So long as the tide advances through a deep ocean, it moves freely and swiftly; but when it passes suddenly from the deep waters of the open ocean to the near-shore shallows, it stumbles upon them, as it were, and the waters are heaped up.[1]

Most persons who mention the pororóca say that it breaks as far up the Amazon as Macapá; and, indeed, the people of Macapa themselves often refer to the rapid cutting away of the riverbanks near their city as the work of the pororóca. It is true that these banks are being rapidly cut down; and it is even a common thing to see, in this part of the country, the stilted houses—the floors being nearly two metres from the ground—that were originally built one, two, or three hundred feet from the water, gradually encroached upon until they fall into the stream. A portion of the old fort at Macapá was, at the time of my visit, about to fall, on account of the land upon which it was built being washed

  1. Prof. Hartt attributes the pororóca a of the Rio Mearim in Maranhão to the form of the channel. It can not be questioned that the form of the channel may modify, and does modify, the force with which the surf strikes the shore; but the single fact of its great violence along the shores between the Araguarý and Cape North, where the whole coast is exposed to the open sea save for the protection offered by shallows, is sufficient to show that form of channel is not its sole cause.