chap. xi. of Recent Origin, 357 



Gregorio, the Pampean deposit, as we have seen, over- 

 lies and fills up furrows in coarse sand, precisely like 

 that now accumulating on the shores near the mouth of 

 the Plata. I can hardly believe that this loose and 

 coarse sand is contemporaneous with the old tertiary 

 and often crystalline strata of the more western parts 

 of the province ; and am induced to suspect that it is 

 of subsequent origin. If that section near Colonia 

 could be implicitly trusted, in which, at a height of 

 only fifteen feet above the Plata, a bed of fresh-looking 

 mussels, of an existing littoral species, appeared to lie 

 between the sand and the Pampean mud, I should con- 

 clude that Banda Oriental must have stood, when the 

 coarse sand was accumulating, at only a little below its 

 present level, and had then subsided, allowing the 

 estuary Pampean mud to cover far and wide its surface 

 up to a height of some hundred feet ; and that after 

 this subsidence the province had been uplifted to its 

 present level. 



In Western Banda Oriental, we know, from two 

 unequivocal sections, that there is a mass, absolutely 

 un distinguishable from the true Pampean deposit, be- 

 neath the old tertiary strata. This inferior mass must 

 be very much more ancient than the upper deposit with 

 its mammiferous remains, for it lies beneath the ter- 

 tiary strata in which all the shells are extinct. Never- 

 theless, the lower and upper masses, as well as some 

 intermediate layers, are so similar in mineralogical 

 character, that I cannot doubt that they are all of 

 estuary origin, and have been derived from the same 

 great source. At first it appeared to me extremely 

 improbable that mud of the same nature should have 

 been deposited on nearly the same spot, during an 

 immense lapse of time, namely, from a period equiva- 

 lent perhaps to the Eocene of Europe to that of the 



