16 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



The writer leaves to his colleague, Doctor Hrdli6ka, all discussion 

 of the anthropologic facts; but the physical evidence leads to con- 

 clusions identical with those indicated by anthropology and leaves 

 no legitimate doubt that geologically ancient man has not yet been 

 found in Argentina. 



General Geologic Description 



WARPED continental SURFACE 



The area which it is necessary to discuss in connection with the 

 problem of the antiquity of man in Argentina comprises the Province 

 of Buenos Aires (pi. 1 and fig. 1) and portions of the provinces and 

 territories adjacent to it on the northwest and southwest. This region 

 is an ancient land surface, many geologic ages having passed since it 

 was submerged beneath the sea. Its mass consists of very old rocks 

 that may be described as quartzites and dolomites, and of still older 

 granite and schists. The marine sediments of comparatively recent 

 geologic date (Mesozoic and Tertiary) that make up a large part of. 

 the Andes are not found in the area, which was an island when the 

 ocean flowed over the site of the Cordillera. 



It is a geologic axiom that any old land is surely worn down by 

 erosion to a plain, unless it is disturbed by the internal forces of the 

 earth in such a manner as to renew the old mountain ranges or to 

 produce new ones. This land of Buenos Aires was thus planed. 

 The plain may be recognized where the ancient rocks are not covered 

 by superficial deposits and it extends no doubt beneath the entire 

 area of the pampas. But that plain, which was once level, is no 

 longer so. Reference is not here made to the plain of the pampas, 

 across which the railroads are graded, but to the eroded surface of 

 the cr3^stalline rocks that lies beneath the superficial deposits of the 

 pampas. At Buenos Aires it is buried to a depth of more than 300 

 meters. Beneath the Rio de la Plata it probably lies still lower. 

 In the mountains of Cordoba, in the Sierra Tandil, and in the Sierra 

 de la Ventana that old plain is raised to an altitude of several hun- 

 dred meters. Thus, that which was formerly nearly level is now 

 depressed or elevated according to the part of the region considered, 

 and we may truly say that the surface of the old land is warped. 



The warping involved changes of altitude. Some areas now stand 

 higher than they did; others lie lower; but the process of erosion 

 tends to restore a flat surface by removing the elevations and filling 

 the hollows. In the sculptured forms of the upraised plains or 

 mountains we may read the history of the uplift. On the other 

 hand, the depressed areas become valleys of great rivers or embay- 

 ments of the sea and, being more or less filled with sediment, contain 

 the record of subsidence in the strata of the deposit. 



