chap. xv. Conglomerate with Silicified Wood. 563 



were found here, all the other species, with the excep- 

 tion of the Pecten, Turritella, and Astarte, have a more 

 ancient aspect than cretaceous forms. On the other 

 hand, taking into account the evidence derived from 

 the cretaceous character of these three shells, and of 

 the Hippurites, Gryphasa orientalis, and Ostrea, from 

 Coquimbo, we are driven back to the provisional name 

 already used of cretaceo-oolitic. From geological 

 evidence, I believe this formation to be the equiva- 

 lent of the Neocomian beds of the Cordillera of Central 

 Chile. 



To return to our section near Las Amolanas : — 

 Above the yellow siliceous sandstone, or the equivalent 

 calcareous slate-rock, with its bands of fossil-shells, 

 according as the one or the other prevails, there is 

 a pile of strata, which cannot be less than from 2,000 

 to 3,000 feet in thickness, in main part composed of 

 a coarse, bright, red conglomerate, with many inter- 

 calated beds of red sandstone, and some of green and 

 other coloured porcelain-jaspery layers. The included 

 pebbles are well rounded, varying from the size of an 

 egg to that of a cricket-ball, with a few larger; and 

 they consist chiefly of porphyries. The basis of the 

 conglomerate, as well as some of the alternating thin 

 beds, are formed of a red, rather harsh, easily fusible 

 sandstone, with crystalline calcareous particles. This 

 whole great pile is remarkable from the thousands of 

 huge, embedded, silicified trunks of trees, one of which 

 was eight feet long, and another eighteen feet in cir- 

 cumference : how marvellous it is, that every vessel in 

 so thick a mass of wood should have been converted 

 into silex ! I brought home many specimens, and all of 

 them, according to Mr. R. Brown, present a coniferous 

 structure. 



Above this great conglomerate, we have from 200 to 

 25 



