38 BUREAU OF AMERICAN JBTHNOLOGY tsuLL. 52 



which is here composed of eolian loess. This loess is assigned to 

 the Upper Pampean and still greater age is allotted to the coquina 

 beneath it. The coquina is riot to be seen in section beneath the 

 loess, but is said to have been struck in numerous wells that were 

 put down through the bluff. This lee, or sheltered place, behind 

 which the coquina occurs, was produced when the waves cut out the 

 Httle bay that is now protected by the quartzite of Punta Piedras, 

 and the eolian deposit, like the coquina, is genetically related to 

 the present strand line. 



The fossil content of the coquina is well known to consist of shells 

 of living species, but is said to include also shells and bones of extinct 

 species. A number of specimens brought by the writer from the 

 localities where he examined the coquina, between Mar del Plata 

 and Necochea, contained shells of living species only. In one 

 fragment a shell of an extinct species was found; the specimen 

 came without a label and the locality from which it was derived 

 could not be identified with certainty. 



In the coquina at Arroyo del Barco, Doctor Hrdlicka and the 

 writer observed a bone which was too firmly imbedded in the rock to 

 be secured, but which appeared to be a jaw or pelvis, possibly of 

 an ungulate. Ameghino stated that the formation contains bones 

 of extinct species peculiar to the Pampean formation (Ensenadean) 

 upon which it rests. In view of the fact that the coast is eroded 

 from this same formation and that any bones contained in it must 

 be washed out and swept along with the beach sands and gravel, 

 it is to be expected that the more massive ones or portions of them 

 may have become imbedded in the coquina. It is said that delicate 

 or articulated bones have been found in the formation. They could 

 hardly survive in such a deposit as that at the Arroyo del Barco, 

 as it is composed of very coarse material which could be moved 

 only by use of considerable force, but the mingled loess and sand 

 of Punta Porvenir might bury lighter objects, either weathered out 

 upon the surface of the underlying Pampean or contemporaneous 

 with the recent deposit. Thus the carapace of the glyptodon 

 found on Punta Porvenir may be a fossil from the older Pampean 

 (Ensenadean) or it may indicate the survival of that species down 

 to the recent time when the coast developed in its present position 

 and the eolian deposit was formed. In this case the paleontologic 

 evidence must derive its significance from the more direct and 

 unequivocal stratigrapliic and physical relations. 



Summary of Geologic Relations 



In the preceding pages the facts which the writer regards as most 

 essential to an understanding of the geology of the region under 

 review have been briefly sketched. They may be summarized as 

 follows : # 



