BASIN OF THE LLANOS. 
84 
the villages of Parapara and Ortiz. It grows very narrow 
in several parts. Basins, the bottoms of which are perfectly 
horizontal, communicate together by narrow passes with 
steep declivities. They were, no doubt, formerly small lakes, 
which, owing to the accumulation of the waters, or some 
more violent catastrophe, have broken down the dykes by 
which they were separated. This phenomenon is found 
in both continents, wherever we examine the longitudinal 
valleys forming the passages of the Andes, the Alps,* or 
the 'Pyrenees.' It is probable, that the irruption of the 
waters towards the Llanos have given, by extraordinary 
rents, the form of ruins to the Morros of San Juan and 
of San Sebastian. The volcanic tract of Parapara and Ortis 
is now only 30 or 40 toises above the Llanos. The eruptions 
consequently took place at the lowest point of the granitic 
chain. 
In the Mesa de Paja, in the ninth degree of latitude, 
we entered the basin of the Llanos. The sun was almost at 
its zenith ; the earth, wherever it appeared sterile and des- 
titute of vegetation, was at the temperature of 48° or 50°.+ 
Not a breath of air was felt at the height at which we were 
on our mules; yet, iu the midst of this apparent calm, 
whirls of dust incessantly arose, driven on t>y those small 
currents of air which glide only over the surface of the 
ground, aud are occasioned by the difference of temperature 
between the naked sand and the spots covered with grass. 
These sand-wiuds augment the suffocating heat of the air. 
Every grain of quartz, hotter than the surrounding air, 
radiates heat in every direction; and it is difficult to ob- 
serve the temperature of the atmosphere, owing to these 
particles of sand striking against the bulb of the thermo- 
meter. All around us the plains seemed to ascend to the 
sky, and the vast and profound solitude appeared like an 
ocean covered with sea- weed. According to the unequal 
mass of vapours diffused through the atmosphere, and the 
variable decrement in the temperature of the different strata 
of air, the horizon in some parts was clear and distinct ; in 
other parts it appeared undulating,, sinuous, and as if striped. 
* For example, the road from the valley of Ursern to the Hospice of 
St. Gothard, and thence to Airolo. 
t A thermometer, placed in the sand, lose to 38*4° and 40° Reaumur- 
