WILLIS] GENERAL GEOLOGIC NOTES 33 



The eastern coast of Argentina is composed, to a great extent, of 

 sea cliffs of the Pampean earths. Many of these are too steep to cHmb 

 and are frequently undercut by the waves that beat against the base. 

 Their height depends on the elevation of the plains and is usually not 

 more than 10 to 15 meters, but in the Barrancas de los Lobos, south 

 of Mar del Plata, the cliffs attain an altitude of 28 meters. (See 

 pi. 6.) As one walks beneath these bluffs of clay and notes the fallen 

 masses of earth disintegrating at the foot of the chff, one can not but 

 recognize that the present coast line is a transient thing. It evidently 

 changes measureably from decade to decade and no feature of it can 

 be many centuries old. Thus no bank or slope or eroded surface 

 between the plain and the beach, nor any deposit built upon such a 

 slope, can be considered to be older than very recent. 



The coastal deposits which may be observed along the recent coast 

 of Buenos Aires are of three kinds: Beach, dune, and coquina forma- 

 tions. The beaches are deposits of sand formed between the base of 

 the cliffs and the sea and are usually so narrow that they are covered 

 by the rising tide. Except as subordinate features at the foot of the 

 bluffs, they are entirely wanting. Sometimes their shoreward limit 

 is formed of dunes. 



Dunes are conspicuous features. These occur wherever there is a 

 source of sand and a surface upon which they can accumulate. They 

 appear to be absent only where the sea cliffs are so steep and high that a 

 dune can not find lodgment. Even then sand is blown into the hollows 

 wrought by wind and waves in the face of the cliff, and lies in banks 

 and festoons which sometimes simulate interbedded sandy strata. 

 The universal activity of the wind and its efficiency in transporting 

 sand constitute most striking facts in the present condition of the 

 coast. The writer's observations cover particularly the stretch from 

 Mar del Plata to Bahia Blanca, but the data regarding the direction 

 and frequency of winds are available for the stretch from Buenos 

 Aires to Bahia Blanca. In his work on the climate of the Republic of 

 Argentina,^ Davis gives two tables, one for Buenos Aires and the other 

 for Bahia Blanca, which embody the results of observations taken 

 three times daily and referred to a scale of 1,000 monthly observations. 

 The original data are arranged with reference to the months and eight 

 points of the compass, namely, north, northeast, east, and so forth. 

 For our purpose we may group these observations into two classes, 

 one representing winds which may be said to blow from the sea, and 

 the other those which blow from the land. The first class comprises 

 winds from northeast, east, southeast, and south, and the second those 



1 Davis, Gualterio G., Clima de la Repilblica Argentina, Buenos Aires, 1909, pp. 41-44, 

 ^535°— Bull. 52—12 3 



