598 Summary of Recent Elevatory part n. 



At a later period, the Pampean mud, of estuary 

 origin, was deposited over a wide area, — in one district 

 conformably on the underlying old tertiary strata, and 

 in another district unconformably on them, after their 

 upheaval and denudation. During and before the 

 accumulation, however, of these old Tertiary strata, 

 and, therefore, at a veiy remote period, sediment, 

 strikingly resembling that of the Pampas, was depo- 

 sited ; showing during how long a time in this case the 

 same agencies were at work in the same area. The 

 deposition of the Pampean estuary mud was accom- 

 panied, at least in the southern parts of the Pampas, 

 by an elevatory movement, so that the M. Hermoso 

 beds probably were accumulated after the upheaval of 

 those round the S. Ventana ; and those at P. Alta after 

 the upheaval of the Monte Hermoso strata ; but there 

 is some reason to suspect that one period of subsidence 

 intervened, during which mud was deposited over the 

 coarse sand of the Barrancas de S. Gregorio, and on the 

 higher parts of Banda Oriental. The mammiferous 

 animals characteristic of this formation, many of which 

 differ as much from the present inhabitants of South 

 America, as do the eocene mammals of Europe from 

 the present ones of that quarter of the globe, certainly 

 co-existed at B. Blanca with twenty species of moll u sea, 

 one balanus, and two corals, all now living in the 

 adjoining sea : this is likewise the case in Patagonia 

 with the jVlacrauckenia, which co-existed with eight 

 shells, still the commonest kinds on that coast. I will 

 not repeat what I have elsewhere said, on the place of 

 habitation, food, wide range, and extinction of the 

 numerous gigantic mammifers, which at this late 

 period inhabited the two Americas. 



The nature and grouping of the shells embedded in 

 the old Tertiary formations of Patagonia and Chile, 



