34§ 
PORTILLO PASS 
CHAP. 
very remarkable. Travellers having observed the difficulty of 
judging heights and distances amidst lofty mountains, have 
generally attributed it to the absence of objects of comparison. 
It appears to me that it is fully as much owing to the trans¬ 
parency of the air confounding objects at different distances, 
and likewise partly to the novelty of an unusual degree of 
fatigue arising from a little exertion,—habit being thus opposed 
to the evidence of the senses. I am sure that this extreme 
clearness of the air gives a peculiar character to the landscape, 
all objects appearing to be brought nearly into one plane, as 
in a drawing or panorama. The transparency is, I presume, 
owing to the equable and high state of atmospheric dryness. 
This dryness was shown by the manner in which woodwork 
shrank (as I soon found by the trouble my geological hammer 
gave me) ; by articles of food, such as bread and sugar, 
becoming extremely hard ; and by the preservation of the 
skin and parts of the flesh of the beasts which had perished 
on the road. To the same cause we must attribute the 
singular facility with which electricity is excited. My flannel- 
waistcoat, when rubbed in the dark, appeared as if it had been 
washed with phosphorus ; every hair on a dog’s back crackled; 
—even the linen sheets, and leathern straps of the saddle, when 
handled, emitted sparks. 
March 23 rd .—The descent on the eastern side of the Cor¬ 
dillera is much shorter or steeper than on the Pacific side ; in 
other words, the mountains rise more abruptly from the plains 
than from the alpine country of Chile. A level and brilliantly 
white sea of clouds was stretched out beneath our feet, shutting 
out the view of the equally level Pampas. We soon entered 
the band of clouds, and did not again emerge from it that day. 
About noon, finding pasture for the animals and bushes for 
firewood at Los Arenales, we stopped for the night. This 
was near the uppermost limit of bushes, and the elevation, I 
suppose, was between seven and eight thousand feet. 
I was much struck with the marked difference between the 
vegetation of these eastern valleys and those on the Chilian 
side : yet the climate, as well as the kind of soil, is nearly the 
same, and the difference of longitude very trifling. The same 
remark holds good with the quadrupeds, and in a lesser degree 
with the birds and insects. I may instance the mice, of which 
