100 
THE PHYSICAL GEOGRAPHY OF THE SEA. 
162. May not, therefore, the whirlwinds which accompany the 
vernal equinox, and sweep over the lifeless plains of the Lower 
Oronoco, take up the "rain dust" which descends in the northern 
hemisphere in April and May ? and may it not be the atmospher- 
ical disturbances which accompany the autumnal equinox that take 
up the microscopic organisms from the Upper Oronoco and the 
great Amazonian basin for the showers of October ? 
163. The Baron von Humboldt, in his Aspects of Nature, thus 
contrasts the wet and the dry seasons there : 
" When, under the vertical rays of the never-clouded sun, the 
carbonized turfy covering falls into dust, the indurated soil cracks 
asunder as if from the shock of an earthquake. If at such times 
two opposing currents of air, whose conflict produces a rotary 
motion, come in contact with the soil, the plain assumes a strange 
and singular aspect. Like conical-shaped clouds, the points of 
which descend to the earth, the sand rises through the rarefied air 
on the electrically-charged centre of the whirling current, resem- 
bling the loud water-spout, dreaded by the experienced mariner. 
The lowering sky sheds a dim, almost straw-colored light on the 
desolate plain. The horizon draws suddenly nearer, the steppe 
seems to contract, and with it the heart of the waiiderer. The 
hot, dusty particles which fill the air increase its sufFocatino- heat 
and the east wind, blowing over the long-heated soil, brings with it 
no refreshment, but rather a still more burning glow. The pools 
which the yellow, fading branches of the fan-palm had protected 
from evaporation, now gradually disappear. As in the icy north 
the animals become torpid with cold, so here, under the influence 
of the parching drought, the crocodile and the boa become mo- 
tionless and fall asleep, deeply buried in the dry mud, ..... 
" The distant palm-bush, apparently raised by the influence of 
the contact of unequally heated and therefore unequally dense 
strata of air, hovers above the ground, from which it is separated 
by a narrow intervening margin. Half concealed by the dense 
clouds of dust, restless with the pain of thirst and hunger, the 
horses and cattle roam around, the cattle lowing dismally, and 
the horses stretching out their long necks and snuffing the wind, 
'if haply a moister current may betray the neighborhood of a not 
wholly dried-up pool 
"At length, after the long drought, the welcome season of the 
rain arrives ; and then how suddenly is the scene changed !...., 
