124 BUREAU OF AMEEICAN ETHNOLOGY [bull. 52 



The Inter-Ensenadean of Piinta Porvenir is a veneer of beach 

 sand and loess spread over an irregular wind-eroded surface of the 

 Ensenadean and slightly cemented by carbonates. It is thickest 

 next the beach and tliins to notliing at a distance of 100 to 110 meters 

 from the beach. It does not extend beyond the reach of spray from 

 storm waves breaking on the point. It lies on a gentle slope, 

 from 4 to 6 meters above the sea, on top of the low bluff cut by 

 the waves in the Ensenadean earth. The face of the bluff is con- 

 cealed by sand blown from the adjacent beach, and this recent 

 sand is continuous with and the same as the Inter-Ensenadean* 

 Both sand and loess have accumulated, though fi'om opposite 

 directions, on the gentle slope to form the Inter-Ensenadean, the 

 sand being blown from the beach, the loess from the bare surface 

 of the Ensenadean that is exposed between the Inter-Ensenadean 

 and the grass-grown plain still higher up. The sand gathers there 

 because there is an eddy or lee on top of the bluff, when the 

 wind blows from the sea. The wind sweeps up the steep face of 

 the bluff, and being directed upward, does not blow directly across 

 the gentle slope that tops the bluff. Sand is blown from the 

 beach against the face of the bluff and accumulates there till a slope 

 of equihbrium is reached, on which a wind can carry it up to the top. 

 It then drops in the wind eddy on the slope. There is a certain sort- 

 ing; black sand, being heavy, remains in larger proportion, whereas 

 white sand, being lighter, is blown away in larger amount. Hence 

 the black sand is more evident in the Inter-Ensenadean. Its 

 presence is a characteristic by which Ameghino identified that for- 

 mation in repeated instances on Punta Porvenir and elsewhere. 

 It is a common constituent of the modern beach sands, which are 

 partly derived from volcanic rocks of northern Patagonia and other 

 districts to the south. 



The loess which gathers to form part of the Inter-Ensenadean is 

 caught in hoUows or is held by moisture. It is blown off of the dry 

 surface of the Ensenadean by land winds and lodges on any moist 

 surface. This process was observed at IVIiramar on the plain close to 

 the sea. The uneven surface had dried unequally and dust, blown 

 into hollows where moisture lingered, was moistened and held. The 

 moisture had evaporated from deposits made in a similar manner 

 a few days or weeks previously, and they were shghtly cemented. 

 They contained specks of black sand and were identified by Doctor 

 Ameghino as Inter-Ensenadean, On Punta Porvenir tlie Inter- 

 Ensenadean is of the same character — a cemented mixture of loess 

 and sand deposited in the zone reached by spray from the sea. It is- 

 thicker and more firmly cemented than the similar accumulations now 

 forming at Aliramar and the mass of it is doubtless older. Lying on 



