566 Valley of Copiapo. part n. 



covered by the upper gypseous strata, which in the 

 section north of the valley are about 6,000 feet in thick- 

 ness, I did not there iusist on this conclusion. 



The pebbles in the above conglomerates, both in 

 the upper and lower beds, are all well rounded, and, 

 though chiefly composed of various porphyries, there 

 are some of red sandstone and of a jaspery stone, both 

 like the rocks intercalated in layers in this same 

 gypseous formation ; there was one pebble of mica- slate 

 and some of quartz, together with many particles of 

 quartz. In these respects there is a wide difference 

 between the gypseous conglomerates and those of the 

 porphyritic- conglomerate formation, in which latter, 

 angular and rounded fragments, almost exclusively 

 composed of porphyries, are mingled together, and 

 which, as already often remarked, probably were ejected 

 from craters deep under the sea. From these facts I 

 conclude, that during the formation of the conglome- 

 rates, land existed in the neighbourhood, on the shores 

 of which the in numerable pebbles were rounded and 

 thence dispersed, and on which the coniferous forests 

 flourished — for it is improbable that so many thousand 

 logs of wood should have been drifted from any great 

 distance. This land, probably islands, must have been 

 mainly formed of porphyries, with some mica-slate, 

 whence the quartz was derived, and with some red sand- 

 stone and jaspery rocks. This latter fact is important, 

 as it shows that in this district, even previously to the 

 deposition of the lower gypseous or cretaceo-oolitic beds, 

 strata of an analogous nature had elsewhere, no doubt 

 in the more central ranges of the Cordillera, been 

 elevated ; thus recalling to our minds the relations of 

 the Cumbre and Uspallata chains. Having already 

 referred to the great lateral valley of the Despoblado, 

 I may mention that above the 2,700 feet of red and 



