WILLIS] 



GENERAL GEOLOGIC NOTES 



17 



In warping, the old land of Buenos Aires on the whole was depressed 

 during a long period. It has recently been raised again, though not 

 to its former general altitude. Tliere were, or are, two regions of 

 greatest depression, one of which is the embayment of the Rio de la 

 Plata, the other the ba}^ of Baliia Blanca; each of these extends far 



Fig. 1. Map of tlie Province of Buenos Aires. 



inland. The intervening area did not sink so deep and within it lie 

 the exceptional zones that were raised and became the Sierras of 

 Cordoba, Tandil, and de la Ventana. 



Over the sinking region superficial deposits of mud were spread, 

 partly by rivers and partly by winds, and these constitute the 

 21535°— Bull. 52—12 2 



