542 Coqutmbo. paet ir. 



district of Arqueros, where a conspicuous hill called 

 Cerro Blanco, formed of a harsh, cream-coloured euritic 

 rock, including a few crystals of reddish feldspar, and 

 associated with some purplish claystone porphyry, seems 

 to fall on a line of elevation. In descending from the 

 Arqueros district, I crossed on the northern border of the 

 valley, strata inclined eastward from the Pluclaro axis : 

 on the porphyritic conglomerate there rested a mass, 

 some hundred feet thick, of brown argillaceous limestone, 

 in parts crystalline, and in parts almost composed of 

 Hippurites Chilensis^ d'Orbig. ; above this came a black 

 calcareous shale, and on it a red conglomerate. In the 

 brown limestone, with the Hippurites, there was an 

 impression of a Pecten and a coral, and great numbers 

 of a large Gryphaea, very like, and, according to Prof. 

 E. Forbes, probably identical with 0. Orientalis y Forbes 

 MS., — a cretaceous species (probably upper greensand) 

 from Verdachellum, in Southern India. These fossils 

 seem to occupy nearly the same position with those at 

 the Puente del Inca, — namely, at the top of the por- 

 phyritic conglomerate, and at the base of the gypseous 

 formation. 



A little above the Hacienda of Pluclaro, I made a 

 detour on the northern side of the valley, to examine 

 the superincumbent gypseous strata, which I estimated 

 at 6,000 feet in thickness. The uppermost beds of the 

 porphyritic conglomerate, on which the gypseous strata 

 conformably rest, are variously coloured, with one very 

 singular and beautiful stratum composed of purple 

 pebbles of various kinds of porphyry, embedded in 

 white calcareous spar, including cavities lined with 

 bright-green crystallised epidote. The whole pile of 

 strata belonging to both formations is inclined, ap- 

 parently from the above-mentioned axis of Pluclaro, 

 at an angle of between 20° and 30° to the east. I will 



