Often the support failed, and they sank to the knees in the slime.
At last, about five o'clock in the evening, the marsh being cleared, the soil regained sufficient firmness, thanks to its clayey nature; but they felt it damp underneath.

Very evidently these lands lay below the neighboring rivers, and the water ran through their pores.
At that time the heat had become overwhelming.

It would even have been unbearable, if thick storm clouds had not interposed between the burning rays and the ground.

Distant lightnings began to rend the sky and low rollings of thunder grumbled in the depths of the heavens.

A formidable storm was going to burst forth.
Now, these cataclysms are terrible in Africa: rain in torrents, squalls of wind which the strongest trees cannot resist, clap after clap of thunder, such is the contest of the elements in that latitude.
Dick Sand knew it well, and he became very uneasy.