III. GENERAL GEOLOGIC NOTES 



By Bailey Willis 



Introductory Note 



The following geologic description is restricted to the writer's 

 observations and to deductions from them. During four months, 

 May to August, 1910, which he spent in Argentina, he visited the 

 vicinity of Buenos Aires, the right bank of ihh Parana as far north 

 as Rosario, the eastern part of the Province of Buenos Aires and the 

 coast from Mar del Plata to Bahia Blanca, and the Sierra de la 

 Ventana; all with reference to studies of the Pampean and post- 

 Pampean terranes. Outside of this region his journevs extended to 

 Tucuman on the north, to San Juan and Mendoza on the west, to 

 Neuquen on the southwest, and to the Rio Colorado, including its 

 delta, on the south. (See maps: Pis. 1 and 21; figs. 1 and 2.) 



The writer is under great obligations to Dr. Florentine Ameghino 

 and also to Prof. Santiago Roth, who not only gave valuable time 

 to accompany his colleague, Doctor Llrdlicka, and himself, but also 

 most generously and frankly discussed the geologic phenomena. 

 Their intimate knowledge and great experience entitle their views 

 to the most serious consideration. Tlie writer is happy to know 

 that in many respects his inferences from observed facts agree with 

 theirs, especially as to the Miocene and Pliocene age of much of the 

 Pampean terrane. 



He regrets that certain geologic relations, when interpreted in the 

 light of his experience in other lands, lead him to conclusions that 

 differ from theirs. There are some points on which they do not agree 

 between themselves, notably as to the classification of the divisions of 

 the Pampean. This problem is one that requires further investigation, 

 both stratigraphically and paleontologically. The superficial forma- 

 tions of the pampas and of the coast are interpreted by the writer 

 as of very recent origin. It is in them that human remains have 

 been found. Were the remains as old as the deposits they would 

 be geologically recent, but they are even j^ounger, since the evidence 

 of occurrence and character in every case that the writers could 

 examine showed that the bodies had been buried in or had accidentally 

 reached the positions in which they were found. 



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