chap. xv. Fossil Shells, 561 



Terebratula aanigma, d'Orbig. (var. of do. E. Forbes, 

 PL V. figs. 13, 14). 



This is the same variety, with that from Guasco, considered by 

 M. d'Orbigny to be a distinct species from his T. senigma, and related 

 to T. obsoleta. 



Plagiostoma and Ammonites, fragments of. 



The lower layers of the limestone contained thou- 

 sands of the Gryphsea; and the upper ones as many 

 of the Turritella, with the Gryphsea (nov. spec.) and 

 Serpulae adhering to them ; in all the layers, the Tere- 

 bratula and fragments of the Pecten were included. 

 It was evident, from the manner in which the species 

 were grouped together, that they had lived where now 

 embedded. Before making any further remarks, I may 

 state, that higher up this same valley we shall again 

 meet with a similar association of shells ; and in the 

 great Despoblado Valley, which branches off near the 

 town from that of Copiapo, the Pecten Dufreynoyi, 

 some Gryphites (I believe G. Darwinii), and the true 

 Terebratula aanigma of d'Orbigny were found together 

 in an equivalent formation as will be hereafter seen. 

 A specimen also, I may add, of the true T. aenigrna, 

 was given me from the neighbourhood of the famous 

 silver mines of Chanuncillo, a little south of the valley 

 of Copiapo, and these mines, from their position, I have 

 no doubt, lie within the great gypseous formation : the 

 rocks close to one of the silver veins, judging from 

 fragments shown me, resemble those singular meta- 

 morphosed deposits from the mining district of Arqueros 

 near Coquimbo. 



I will reiterate the evidence on the association of 

 these several shells in the several localities. 



