chap. xv. Valley of the Despoblado. 573 



moisture ; and this no doubt must have been a sheet of 

 water. A lake at this great height, and without a 

 barrier on any one side, is out of the question ; conse- 

 quently we must conclude that the tufaceous matter 

 was anciently deposited beneath the sea. It was cer- 

 tainly deposited before the excavation of the valleys, or 

 at least before their final enlargement ; ] and I may 

 add, that Mr. Lambert, a gentleman well acquainted 

 with this country, informs me, that in ascending the 

 ravine of Santandres (which branches off from the Des- 

 poblado) he met with streams of lava and much erupted 

 matter capping all the hills of granite and porphyry, 

 with the exception of some projecting points ; he also 

 remarked that the valleys had been excavated subse- 

 quently to these eruptions. 



This volcanic formation, which I am informed by 

 Mr. Lambert extends far northward, is of interest, as 

 typifying what has taken place on' a grander scale on 

 the corresponding western side of the Cordillera of 

 Peru. Under another point of view, however, it pos- 

 sesses a far higher interest, as confirming that conclu- 

 sion drawn from the structure of the fringes of stratified 

 shingle which are prolonged from the plains at the foot 

 of the Cordillera far up the valleys,-— namely, that this 

 great range has been elevated in mass to a height of 

 between 8,000 and 9,000 feet; 2 and now, judging from 

 this tufaceous deposit, we may conclude that the hori- 



1 I have endeavoured to show in my • Journal,' &c. (2nd edit.) 

 p. 355, that this arid valley was left by the retreating sea, as the 

 land slowly rose, in the state in which we now see it. 



2 I may here mention that on the south side of the main valley 

 of Copiapo, near Potrero Seco, the mountains are capped by a thick 

 mass of horizontally stratified shingle, at a height which I estimated 

 at between 1,500 and 2,000 feet above the bed of the valley. This 

 shingle, I believe, forms the edge of a wide plain, which stretches 

 southwards between two mountain ranges. 



