552 Valley of Copiapo. paetil 



many brown-coloured dikes, running north and south. 

 Above the town, the main valley runs in a south-east 

 and even more southerly course towards the Cordillera, 

 where it is divided into three great ravines, by the 

 northern one of which, call Jolquera, I penetrated for a 

 short distance. The coloured section, fig. 3 in Plate I., 

 gives an eye-sketch of the structure and composition 

 of the mountains on both sides of this valley : a straight 

 east and west line from the town to the Cordillera is 

 perhaps not more than thirty miles, but along the 

 valley the distance is much greater. Wherever the 

 valley trended very southerly, I have endeavoured to 

 contract the section into its true proportion. This 

 valley, I may add, rises much more gently than any 

 other valley which I saw in Chile. 



To commence with our section, for a short distance 

 above the town we have hills of the granitic series, 

 together with some of that rock [A], which I suspect to 

 be altered clay-slate, but which Prof. Gr. Rose, judg- 

 ing from specimens collected by Meyen at P. Negro, 

 states is serpentine passing into greenstone. We then 

 come suddenly to the great Gypseous formation [B] 

 without haviug passed over, differently from in all the 

 sections hitherto described, any of the porphyritic con- 

 glomerate. The strata are at first either horizontal or 

 gently inclined westward ; then highly inclined in 

 various directions, and contorted by underlying masses 

 of intrusive rocks ; and lastly, they have a regular east- 

 ward dip, and form a tolerably well pronounced north 

 and south line of hills. This formation consists of 

 thin strata, with innumerable alternations, of black, 

 calcareous slate-rock, of calcareo-aluminous stones like 

 those at Coquimbo, which I have called pseudo-hone- 

 stones, of green jaspery layers, and of pale-purplish 

 calcareous, soft rottenstone, including seams and veins 



