308 GEOLOGY OF THE COEDILLERA. [CHAP. xv. 



forced home on the mind of the geologist, that nothing, not even 

 the wind that blows, is so unstable as the level of the crust of this 

 earth. 



I will make only one other geological remark: although the 

 Porfcillo chain is here higher than the Peuquenes, the waters, 

 draining the intermediate valleys, have burst through it. The 

 same fact, on a grander scale, has been remarked in the eastern 

 and loftiest line of the Bolivian Cordillera, through which the 

 rivers pass : analogous facts have also been observed in other 

 quarters of the world. On the supposition of the subsequent and 

 gradual elevation of the Portillo line, this can be understood ; for 

 a chain of islets would at first appear, and, as these were lifted up, 

 the tides would be always wearing deeper and broader channels 

 between them. At the present day, even in the most retired 

 Sounds on the coast of Tierra del Fuego, the currents in the 

 transverse breaks which connect the longitudinal channels, are 

 very strong, so that in one transverse channel even a small vessel 

 under sail was whirled round and round. 



About noon we began the tedious ascent of the Peuquenes ridge, 

 and then for the first time experienced some little difficulty in our 

 respiration. The mules would halt every fifty yards, and after 

 resting for a few seconds the poor willing animals started of their 

 own accord again. The short breathing from the rarefied atmo- 

 sphere is called by the Chilenos "puna;" and they have most 

 ridiculous notions concerning its origin. Some say " all the waters 

 here have puna ; " others that " where there is snow there is puna ; " 

 and this no doubt is true. The only sensation I experienced was 

 a slight tightness across the head and chest, like that felt on leaving 

 a warm room and running quickly in frosty weather. There was 

 some imagination even in this; for upon finding fossil shells on 

 the highest ridge, I entirely forgot the puna in my delight. 

 Certainly the exertion of walking was extremely great, and the 

 respiration became deep and laborious : I am told that in Potosi 

 (about 13,000 feet above the sea) strangers do not become 

 thoroughly accustomed to the atmosphere for an entire year. 

 The inhabitants all recommend onions for the puna; as this 

 vegetable has sometimes been given in Europe for pectoral com- 

 plaints, it may possibly be of real service : for my part I found 

 nothing so good as the fossil shells ! 



