1835.] DRY AND CLEAR ATMOSPHERE. 325 
several broad fields of perpetual snow. These frozen masses, 
during the process of thawing, had in some parts been converted 
into pinnacles or columns,* which, as they were high and close 
together, made it difficult for the cargo mules to pass. On 
one of these columns of ice, a frozen horse was sticking as on 
a pedestal, but with its hind legs straight up in theair. The 
animal, I suppose, must have fallen with its head downward 
into a hole, when the snow was continuous, and afterwards the 
surrounding parts must have been removed by the thaw. 
When neariy on the crest of the Portillo, we were enveloped 
in a falling cloud of minute frozen spicula. This was very un- 
fortunate, as it continued the whole day, and quite intercepted 
our view. The pass takes its name of Portillo, from a narrow 
cleft or doorway on the highest ridge, through which the road 
passes. From this point, on a clear day, those vast plains which 
uninterruptedly extend to the Atlantic Ocean, can be seen. We 
descended to the upper limit of vegetation, and found good 
quarters for the night under the shelter of some large fragments 
of rock. We met here some passengers, who made anxious in- 
quiries about the state ofthe road. Shortly after it was dark 
the clouds suddenly cleared away, and the effect was quite ma- 
gical. The great mountains, bright with the full moon, seemed 
impending over us on all sides, as over a deep crevice: one 
morning, very early, I witnessed the same striking effect. As 
soon as the clouds were dispersed it froze severely ; but as there 
was no wind, we slept very comfortably. 
The increased brilliancy of the moon and stars at this eleva- 
tion, owing to the perfect transparency of the atmosphere, was 
very remarkable. ‘Travellers having observed the difficulty o1 
judging heights and distances amidst lofty mountains, have gene- 
rally attributed it to the absence of objects of comparison. It 
appears to me, that it is fully as much owing to the transparency 
of the air confounding objects at different distances, and likewise 
* This structure in frozen snow was long since observed by Scoresby in 
the icebergs near Spitzbergen, and lately, with more care, by Colonel 
Jackson (Journ. of Geograph. Soc., vol. v. p. 12) on the Neva. Mr. Lyell 
oe vol. iv. p. 860) has compared the fissures, by which the co- 
umaar structure seems to be determined, to the joints that traverse nearly 
all rocks, but which are best seen in the non-stratified masses. I may 
observe, that in the case of the frozen snow, the columnar structure must be 
owing to a “metamorphic” action, and not to a process during deposition. 
