When this takes place, the rending of the indurated soil is sudden and violent, as if from the shock of an earthquake. If at such a time two opposing currents of air, whose conflict produces a rotatory motion, come in contact with the surface of the earth, the Llanos assume a strange and singular aspect. Like cone-shaped clouds, whose extremities seem to touch the ground, the sand rises through the rarefied air in the electrically-charged centre of the whirling current; like the sand-spouts of the Saharan Desert, or the waterspouts which formerly were the awe and dread of the mariner. Then does the lowering sky cast a "dim uncertain light," like a November fog in London, on the desolate plain. The horizon draws suddenly nearer; the Steppe seems to contract, and a nameless terror seizes the heart of the wanderer. The hot dusty air increases in suffocating heat; and the east wind, blowing over the long-heated soil, yields no refreshment, but rather oppresses with its burning glow. The pools, hitherto protected from evaporation by the yellow fading branches of the fan palm, begin to disappear. As in the north the animals grow torpid with the mortal cold, so under the influence of the parching drought the boa and the crocodile fall asleep, buried deeply in the dry mud. Everywhere the drought prevails, and yet everywhere the refracted rays of light delude the traveller with the image of gleaming lakes and rushing rivers. The distant palm bush hovers above the ground like a spectre, apparently raised by the influence of the contact of unequally heated, and, therefore, unequally dense strata of air. Half hidden by the rolling clouds of dust, restless with the pangs of thirst and hunger, the horses and cattle roam around, the cattle dismally lowing, and the horses stretching out their long necks and snuffing the wind, in the hope some moister current may betray the neighbourhood of a not wholly failing pool. More sagacious and astute, the wary mule seeks a different mode of alleviating his thirst. Under its prickly envelope the melon-cactus conceals a watery pith. The mule first strikes the prickles aside with his fore-feet, and then cautiously approaches his lips to the plant and drinks the cool juice. But the experiment is not always without danger, and many animals are lamed by the spines of the cactus.