57 2 Copiapo. 



pajlt n. 



zontally stratified, tufaceous deposit. The lowest bed 

 is of a pale purple colour, hard, fine-grained, and full 

 of broken crystals of feldspar and scales of mica. The 

 middle bed is coarser, and less hard, and hence weathers 

 into very sharp pinnacles ; it includes very small frag- 

 ments of granite, and innumerable ones of all sizes of 

 gray vesicular trachyte, some of which were distinctly 

 rounded. The uppermost bed is about 200 feet in 

 thickness, of a darker colour and apparently hard ; but 

 I had not time to ascend to it. These three horizontal 

 beds may be seen for the distance of many leagues, 

 especially westward or in the direction of the Pacific, 

 capping the summits of the mountains, and standing on 

 the opposite sides of the immense valleys at exactly 

 corresponding heights. If united they would form a 

 plain, inclined very slightly towards the Pacific ; the 

 beds become thinner in this direction, and the tuff 

 (judging from one point to which I ascended, some 

 way down the valley) finer-grained and of less specific 

 gravity, though still compact and sonorous under the 

 hammer. The gently inclined, almost horizontal 

 stratification, the presence of some rounded pebbles, 

 and the compactness of the lowest bed, though render- 

 ing it probable, would not have convinced me that this 

 mass had been of subaqueous origin, for it is known 

 that volcanic ashes falling on land and moistened by 

 rain often become hard and stratified ; but beds thus 

 originating, and owing their consolidation to atmo- 

 spheric moisture, would have covered almost equally 

 every neighbouring summit, high and low, and would 

 not have left those above a certain exact level abso- 

 lutely bare ; this circumstance seems to me to prove 

 that the volcanic ejections were arrested at their pre- 

 sent, widely extended, equable level, and there con- 

 solidated by some other means than simple atmospheric 



