COQUIMBO TO GUASCO.
The rocks near the coast, and some way inland, do not differ from those described northwards of Valparaiso: 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 composing an imperfect gneiss. There are two large districts of mica-schists, passing into glossy clay-slate, and resembling 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 collection 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:—
Turritella Andii, d’Orbigny, “Voyage” Part Pal. Pecten Dufreynoyi, d’Orbigny, “Voyage” Part Pal. Terebatula ignaciana, d’Orbigny, “Voyage” Part Pal.
The relations of these species have been given under the head of Coquimbo.
Terebratula aenigma, d’Orbigny, “Voyage” Part Pal.
This shell M. d’Orbigny does not consider identical with his T. aenigma, but near to T. obsoleta. Professor Forbes thinks that it is certainly a variety of T. aenigma: we shall meet with this variety again at Copiapo.
Spirifer Chilensis, E. Forbes.
Professor Forbes remarks that this fossil resembles several carboniferous limestone Spirifers; and that it is also related to some liassic species, as S. Wolcotii.
If these shells had been examined independently of the other collections, they would probably have been considered, from the characters of the two Terebratulae, and from the Spirifer, as oolitic; but considering that the first species, and according to Professor Forbes, the four first, are identical with those from Coquimbo, the two formations no doubt are the same, and may, as I have said, be provisionally called cretaceo-oolitic.