chap. xv. Valley of the Despoblado* 571 



blended together and the basis rendered porphyritic ; 

 these beds separated distinct streams, from sixty to 

 eighty feet in thickness, of clay-stone lavas. Near 

 Paipote, also, there was much true porphyritic breccia- 

 conglomerate : nevertheless, few of these masses were 

 metamorphosed to the same degree with the corre- 

 sponding formation in Central Chile. I did not meet in 

 this valley with any true andesite, but only with im- 

 perfect andesitic porphyry ^ including large crystals of 

 hornblende : numerous as have been the varieties of 

 intrusive porphyries already mentioned, there were here 

 mountains composed of a new kind, having a compact, 

 smooth, cream-coloured basis, including only a few 

 crystals of feldspar, and mottled with dendritic spots of 

 oxide of iron. There were also some mountains of a 

 porphyry with a brick-red basis, containing irregular, 

 often lens-shaped, patches of compact feldspar, and 

 crystals of feldspar, which latter to my surprise I find 

 to be orthite. 



At the foot of the first ridge of the main Cordillera, 

 in the ravine of Maricongo, and at an elevation which, 

 from the extreme coldness and appearance of the vege- 

 tation, I estimated at about 10,000 feet, I found beds of 

 white sandstone and of limestone including the Peden 

 Dufreynoyi, Terebratula cenigma, and some Gryphites. 

 This ridge throws the water on the one hand into the 

 Pacific, and on the other, as I was informed, into a 

 great gravel-covered, basin-like plain, including a salt- 

 lake, and without any drainage-exit. In crossing the 

 Cordillera by this Pass, it is said that three principal 

 ridges must be traversed, instead of two, or only one as 

 in Central Chile. 



The crest of this first main ridge and the surround- 

 ing mountains, with the exception of a few lofty 

 pinnacles, are capped by a great thickness of a hori- 



