112 BUREAU OF AMERICAN ETHNOLOGY [bull. 52 



has often been so great that the older geologic sediments are exposed, 

 and bones of extmct species of animals lying in these sediments 

 become more or less visible or even loose; in other instances, how- 

 ever, the erosion has been relatively slight, amounting to but a few 

 inches below recent surface. 



A third and most characteristic feature of the coast consists of 

 the sand dunes, or medanos, which line the shore for great dis- 

 tances. They form a range of sand hills which, as the sea advances 

 steadily and, in general, with considerable rapidity at the expense 

 of the land, must be quite recent in their present location. This 

 line of dunes varies from less than a mile to several miles in breadth 

 and continues, with a few interruptions, from a short distance 

 south of Mar del Plata to Bahia Blanca. The prevailing height of 

 the individual dunes ranges from about 30 to 80 feet, but occasion- 

 ally they are lower or higher. They are of various shapes, the coni- 

 cal and "hog-back" types predominating, differ considerably in 

 bulk, and extend in many cases close to the beach. In some parts, 

 as at Monte Hermoso, the sea front presents a barranca face sur- 

 mounted by the medanos. 



The sand dunes are of two principal varieties and the difference 

 between them is of consequence archeologically. The first class, 

 preponderant north of Monte Hermoso, are the barren, moving 

 dunes, while the second consist of such sand hills as have become 

 covered and more or less fixed by vegetation. It is the region of 

 the barren medanos that is especially interesting anthropologically. 

 In the fixed dunes whatever implements and other remains of aborig- 

 inal population there may be, lie buried within or under the sand and 

 with rare exceptions escape observation. Among the barren and 

 moving dunes, on the other hand, the force of the winds results in 

 uncovering the implements and other remains, and these remain for a 

 longer or shorter time exposed to view, so that they may be easily 

 collected. 



The barren dunes are shifted by the sand being blown from the 

 slope exposed to the wind and falling down the opposite slope. On 

 the exposed side the wind tends to remove all the sand down to the 

 more resistant surface of the ground. If there are any stones, imple- 

 ments, or heavier human or animal remains anywhere in the sand or 

 on the ground underneath, such objects sink down to, or remain in 

 place on, the exposed harder surface, to be reburied, reexposed, and 

 shifted from time to time as the wind currents assume different 

 directions. 



All the dunes connect at the base and inclose more or less extensive 

 hollows. Some of these hollows are relatively shallow, circum- 

 scribed, and sandy. Other depressions are, however, much larger 



