26 BtJEEAtr OF AMERICAN ETHNOLOGY [bull. 52 



but the surface of the ground during that interval appears not to 

 have differed from the present surface. The writer regards this tosca 

 zone as evidence of a drier epoch antedating the present relatively 

 huniid one. 



Tosca occurs irregularly at other levels or without reference to a 

 particular level in the loess deposits. Some of it has been displaced 

 and reburied; some has been washed and rolled. It is evident that 

 local conditions have favored the deposition of secondary lime at 

 various times, if not usually, throughout that part of the Pampean 

 period which is represented by this section. But during two epochs 

 the relations of surface- and ground-water level were particularly con- 

 stant for a sufficient time in each case to produce especially heavy 

 deposits. The first of these epochs coincides with the period of 

 passage from the alluvial deposition represented by the dark-brown 

 earth at the base to the period of aridity that succeeded. The second 

 does not correspond with any time-interval observed in the section, 

 but with a later episode. 



The interpretation of the Barrancas del Norte which the deposits 

 and contacts suggest to the writer may therefore be provisionally 

 stated as follows : 



The (n+1) episode Brown earthy loess — alluvial humid 



The (n+2) episode Wind erosion— tosca formation semiarid 



The (n+3) episode Lacustrine ' humid 



The (n+4) episode Wind erosion and loess deposits semiarid to arid 



The (n+5) episode Tosca formation semiarid 



The (n+6) episode Black earth humid 



In this section Ameghino distinguishes three distinct deposits, 

 which he has named Ensenadean, Bonaerean, and Belgranean. 

 The writer likewise recognizes tliree episodes of deposition, namely, 

 the (n + 1), (n + 3), and (n + 4) divisions of the above climatic scale. 

 The criteria on which he bases his divisions are, however, not of a 

 character to permit him to correlate them with the formations at the 

 type localities from which they are named by Ameghino. He feels, 

 moreover, that the criteria by which to distinguish the climatic divi- 

 sions of Pampean time require further study before complete confi- 

 dence can be placed in the conclusions. 



The characteristics which mark the Pampean terrane in th« section 

 of the Barrancas del Norte may be recognized in numerous other sec- 

 tions along the coast: For instance, at the Barrancas de los Lobos, 

 south of Mar del Plata, near Miramar, near Necochea, and also at 

 Monte Hermoso (a few miles east of Bahia Blanca). The basal 

 stratum exposed in the Barrancas del Norte may be traced to the 

 Barrancas de los Lobos, where it lies in the upper part of the cliffs 

 above some 10 meters of similar material, which is exposed between 

 it and the sea. The lower formation is somewhat darker in color 



