16 F, Ameghino — Geology of Argentina. 



shown well developed at Punta Arenas, covering in some parts the 

 layers of lignite. The collection of fossil mollusca from this locality 

 studied by Philippi, comes from this same horizon, with the single 

 exception of Ostrea Patagoyiica, and all the species are considered by 

 this distinguished malacologist to be extinct, and consequently as 

 representing an Eocene fauna. 



Now, it is also evident that that marine deposit (supra-Patagonian 

 zone) and the Upper Santacruzian horizon form part of one and the 

 same epoch, for in the lower portion of this terrestrial formation 

 there are intercalated marine bands of the lower zone with Ostrea 

 Boiirgeoisi and other chai'acteristic fossils of the same beds, resting 

 upon deposits with remains of Astrapotherium, Homalodontothermm, 

 JProterotherium, Homiinculus, and all the other representatives of the 

 marvellous mammal fauna of the Santa Cruz Formation. 



We conclude from this, that the Santa Cruz Formation, and nearly 

 the whole of the Patagonian Formation, represent in our country the 

 complete series of the Eocene strata; while the lower and more 

 ancient part of the Patagonian Formation, with the Pyrotherium beds 

 which are found below it, corresponds with a portion of the Upper 

 Cretaceous. 



The Boulder Formation. 



Above the earlier formations there come great sheets of basalt, and 

 where this is wanting there is found the formation of Patagonian 

 boulders, which, covering also the basalts, extend over the whole 

 surface of Patagonia, both over the plateaux and over the slopes of 

 the valleys ; though the true boulder formation is that which covers 

 the plateaux. The boulder deposits of the sides and the bottom of 

 the valleys are the result of the falling down and transport at a com- 

 paratively modern period of the pebbles and boulders of the deposit 

 ■which extends over the plateaux, and this is the only one with which 

 I am concerned. 



This dei^osit, perhaps the most gigantic boulder formation known 

 on the surface of the earth, constitutes up till now a geological 

 enigma. Of marine origin accoi'ding to Darwin, who believed that 

 nothing but the ocean could produce such a dispersion of boulders 

 with the uniformity it presents, it has been regarded by almost all 

 later authors as a product of the Glacial epoch. There is likewise 

 difference of opinion as to the epoch to which it ought to be referred : 

 Pampean according to some, it is of more recent date according to 

 others, while there are not wanting those who believe that it 

 immediately preceded the Pampean Formation. 



In 1889,^ relying on the data provided by C. Ameghino, which 

 showed this formation to be in part derivative, with the materials 

 appearing as if they had been rolled by water, and no trace of strias 

 or glacial polish or angular fragments which could have been trans- 

 ported by ice, I arrived at the conclusion that we were dealing with 

 an accumulation produced by water without the intervention of 

 glacial agencies. I recognized also that this accumulation might 



1 F. Ameghijio, *■ Contrib. Conoc. Mamif. Fos. Kepub. Argent.," p. 36. 



