chap. xi. Bahia Blanca. 323 



surrounding plains must have been under water, were 

 the strata at Monte Hermoso depositing at the bottom 

 of a great open sea, between 800 and 1,000 feet in 

 depth ? I much doubt this ; for if so, the almost per- 

 fect carcasses of the several small rodents, the remains 

 of which are so very numerous in so limited a space, 

 must have been drifted to this spot from the distance 

 of many hundred miles. It appears to me far more 

 probable, that during the Pampean period this whole 

 area had commenced slowly rising (and in the cliffs, at 

 several different heights, we have proofs of the land 

 having been exposed to sea-action at several levels), and 

 that tracts of land had thus been formed of Pampean 

 sediment round the Ventana and the other primary 

 ranges, on which the several rodents and other quadru- 

 peds lived, and that a stream (in which perhaps the 

 extinct aquatic Hydrochcerus lived) drifted their bodies 

 into the adjoining sea, into which the Pampean mud 

 continued to be poured from the north. As the land 

 continued to rise, it appears that this source of sediment 

 was cut off; and in its place sand and pebbles were 

 borne down by stronger currents, and conformably de- 

 posited over the Pampean strata. 



Punta Alta is situated about thirty miles higher up 

 on the northern side of this same bay : it consists of 

 a small plain, between twenty and thirty feet in height, 

 cut off on the shore by a line of low cliffs about a mile 

 in length, represented in the diagram with its vertical 

 scale necessarily exaggerated. The lower bed (A) is 

 more extensive than the upper ones ; it consists of 

 stratified gravel or conglomerate, cemented by calcareo- 

 arenaceous matter, and is divided by curvilinear layers 

 of pinkish marl, of which some are precisely like tosca- 

 rock, and some more sandy. The beds are curvilinear, 

 owing to the action of currents, and dip in?' different 

 15 



