34 



BUREAU OF AMERICAN ETHNOLOGY 



[bull. 5i 



from soutluvest, west, northwest, ami nortli. The figures taken from 

 Davis's tables then 3-iehl the following: 



These figures show that at Buonos Aires the wintls blow far more 

 frequently from the sea than from the lantl, whereas at Bahia Blanca 

 the reverse is the case. Davis comments on tliis fact and states that 

 if the data were to be given for a number of intermediate stations it 

 would be seen that the variation in frequency of the winds changes 

 from north to south in a regular manner in obedience to a physical 

 law. An examination of the isobaric and isothermal charts for ditTer- 

 ent seasons, accomjKiuying Davis's work, shows clearly the nature of 

 this law and its relation to the observed variation. According to the 

 same official source of information, the mean annual velocity of the 

 wind at Buenos .Vires is 15.8 kilometers per hour and there is no 

 month in the year in wliich the mean monthly velocity falls below 13 

 kilometers per hour. At Baliia Blanca the annual mean is 14.9 and 

 the least monthly mean is 10.2. 



The eft'ect of the barometric and thermometric conditions is to 

 produce winds which, along the northeastern cofist of the Province 

 of Buenos Aires, blow prevailmgly on shore, and this condition 

 extends to a point south of ^lar del Plata. The coast then trends 

 away southwest, while the prevailing direction of the wind veers m 

 the same direction, but through even a gi'eater angle, so that as we 

 go from Mar del Plata southwestward toward Bahia Blanca the pre- 

 vaihng winds blow more and more nearly in a dkection parallel to 

 the coast. The effect of these rehitions on the work of the wmd is 

 seen in the distribution of sand dunes, wliich become high and 

 numerous and occupy a relatively broad belt along this shore where- 

 ever the sea clifTs do not prevent. ^* 



By reference to the local description of the coast northeast of 

 Necochea it will be seen that there are older and younger dunes, wluch 



