There were tracts of moist ground, sometimes covered with tall forest-trees, at others opening out into a sedgy morass, with perhaps a small lake or water-patch in the centre.
The first required them to make way through mud, or thick stagnant water covered with scum, often reaching above their knees.

These places were especially disagreeable to cross; for under the gloomy shadow of the trees they would now and then catch a glimpse of huge newt-like lizards of the genus _hydrosaurus_--almost as large as crocodiles--slowly floundering out of the way, as if reluctant to leave, and half-determined to dispute the passage.
Moreover, while thus occupied, they lived in the obscurity of an eternal twilight, and could travel only by guess-work.

They had no guide save the sun, which in these shadows is never visible.

Through the thick foliage overhead its disc could not be seen; nor aught that would enable them to determine its position in the sky, and along with it their direction upon the earth.

It was, therefore, not only a relief to their feelings, but a positive necessity for their continuance in the right direction, that now and then a stretch of open swamp obstructed their track.