30 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



topographic mapping. Nevertheless, the wind origin of the surface 

 features of the pampas is obvious in the general form of the hollows 

 and swells. Anyone who has studied a loess-covered landscape knows 

 the long sweep from plain to mountain which is the characteristic 

 form of equilibrium that is produced where the wind is deflected 

 upward from the plain. Like the slope of equilibrium of the beach it 

 varies in declivity with the material and the force of the movmg ele- 

 ment, and like the drumloid curve produced by ice it is definitely 

 characteristic of the fashioning medium. The pampas everywhere 

 bear the impress of the wind which has scoured, hollowed, and molded 

 their vast flat expanses of fine brown earth. 



The surface which is thus characterized as an effect of wind sculp- 

 ture is modified along the right bank of the Parana, in what is now 

 the most humid region of the Province of Buenos Aires, by stream 

 erosion. A number of small valleys have their rise in the pampa and 

 extend more or less directly to the river. Those which the writer has 

 particularly examined are at Alvear and Ramallo ; another is crossed 

 by the railroad near Baradero. These are but examples of similar 

 valleys of erosion which occasion the frequent up and down grades on 

 the Ferrocarril Central between Buenos Aires and Rosario. The 

 Arroyo de Ramallo is characteristic. (PL 4.) 



The Arroyo de Ramallo debouches into the Parana with a low flood 

 plain about a kilometer in width. Between 2 and 3 kilometers from 

 the Parana the little valley is much narrower and is bordered by 

 steep banks and low bluff's. A kilometer higher up the stream has 

 been dammed and affords a fall of about 3 meters. Its channel 

 extends a very considerable distance farther back into the plain, but 

 only as a shallow talweg. 



The little valleys of which the Arroyo de Ramallo is a type are in 

 an early stage of development. They are due to little confluent 

 autogenous streams that have grown back from the Parana into the 

 pampas and as yet have reached no more than a youthful growth. 

 Their history embodies, it is true, the early episode of erosion, which 

 was followed by partial filling with eolian loess, and most recently by 

 reexcavation of the talweg, but when we consider the softness of the 

 Pampean earths as opposed to the eroding power of a stream, we are 

 obliged to recognize that these little streams have accomplished but 

 a small amoimt of erosion. 



In the photograph shown in plate 5, we see the bank of the Parana 

 at San Lorenzo, above Rosario. The level Pampean plain extends at 

 an elevation of 12 to 15 meters above the river and ends in nearly 

 vertical bluffs, which are scarcely attacked by erosion. Talus is also 

 wanting and the scarp is very young. It overlooks the wide channel 



