That singular phenomenon known as the _Gapo_ (or _Ygapo_), and which is one of the most remarkable characteristics of the great Amazonian region, demands a more detailed description. It is worthy of this, as a mere study of physical geography,--perhaps as pleasant a science as any; and furthermore, it is here absolutely necessary to the understanding of our tale. Without some comprehension of the circumstances that surrounded them, the hardships and sufferings endured, the adventures accomplished, and the perils passed by the crew of the strayed galatea, would appear as so many fabulous inventions, set forth to stimulate and gratify a taste for the merely marvellous. Young reader, this is not the aim of your author, nor does he desire it to be the end. On the contrary, he claims to draw Nature with a verisimilitude that will challenge the criticism of the naturalist; though he acknowledges a predilection for Nature in her wildest aspects,--for scenes least exposed to the eye of civilization, and yet most exposed to its doubting incredulity. There are few country people who have not witnessed the spectacle of a piece of woodland inundated by the overflow of a neighboring stream. This flood is temporary; the waters soon subside into their ordinary channel, and the trees once more appear growing out of _terra firma_, with the green mead spreading on all sides around them. But a flooded forest is a very different affair; somewhat similar in character indeed, but far grander. Not a mere spinney of trees along the bank of a small stream; but a region extending beyond the reach of vision,--a vast tract of primeval woods,--the tall trees submerged to their very tops, not for days, nor weeks, but for months,--ay, some of them forever! Picture to your mind an inundation of this kind, and you will have some idea of the Gapo.