550 Coquimbo to Guasco. paet it. 



formation. Considering this resemblance, and that the 

 fossils from the Puente del Inca at the base of the 

 gypseous formation, and throughout the greater part of 

 its entire thickness on the Peuquenes range, indicate 

 the Neocomian period, — that is, the dawn of the cre- 

 taceous system, or, as some have believed, a passage be- 

 tween this latter and the oolitic series — I conclude that 

 probably the gypseous and associated beds in all the 

 sections hitherto described, belong- to the same great 

 formation, which I have denominated — cretaceo-oolitic. 

 I may add, before leaving Coquimbo, that M. Gay found 

 in the neighbouring Cordillera, at the height of 14,000 

 feet above the sea, a fossiliferous formation, including a 

 Trigonia and Pholadomya ; 1 — both of which genera 

 occur at the Puente del Inca. 



Coquimbo to Guasco, — The rocks near the coast, 

 and some way inland, do not differ from those described 

 northwards of A^alparaiso : we have much greenstone, 

 syenite, feldspathic and jaspery slate, and grauwackes 

 having a basis like that of claystone; there are some 

 large tracts of granite, in which the constituent 

 minerals are sometimes arranged in folia, thus compos- 

 ing an imperfect gneiss. There are two large districts 

 of mica-schist, passing into glossy clay-slate, and re- 

 sembling the great formation in the Chonos Archipelago. 

 In the valley of Guasco, an escarpment of porphyritic 

 conglomerate is first seen high up the valley, about two 

 leagues eastward of the town of Ballenar. I heard of a 

 great gypseous formation in the Cordillera ; and a col- 

 lection of shells made there was given me. These 

 shells are all in the same condition, and appear to have 

 come from the same bed : they consist of — 



1 D'Orbigny, ' Voyage, Part. Geolog,' p. 242. 



