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 the air. 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 nearly 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 of the 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 01 

 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 

 (Principles, vol. iv. p. 360) has compared the fissures, by which the co- 

 lumnar 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. 



