FOSSIL MAMMALIA. o 



On the shores of the Plata and in the neighbouring districts, proofs of a 

 change of level having taken place between the land and the water within a recent 

 period, may be observed. Both near Monte Video and Colonia del Sacramiento, 

 beds of shells are lying on the beach at the height of several feet above the pre- 

 sent tidal action. Near Maldonado I saw estuary shells of recent species embed- 

 ded in clay, and raised above the level of a neighbouring fresh-water lake. 



On the banks of the Parana, a shell identical with, or most closely resembling 

 an estuary species (Potamomya labiata, now living in that part of the Plata, 

 where the water is brackish) is accumulated in great masses, which are found 

 some miles inland, and are elevated several yards above the level of the river. 

 Sir Woodbine Parish, also, has in his possession, shells procured from an exten- 

 sive formation near Ensenada de Barragan (south of Buenos Ay res), which is 

 quarried for lime. Mr. George Sowerby has examined these fossils, and says the 

 following are identical with living kinds ; Voluta colocynthis, Dillwyn : V. angu- 

 lata, Swainson : Buccinum globulosum, Kiener : a variety of Oliva patula : a 

 Cythercea closely resembling or identical with C. fiexuosa, and a fragment of a 

 second species, probably C purpurascens ; Potamomya labiata ; and fragments of 

 oysters. There is, however, a species of Mactra in very great numbers, with 

 which Mr. Sowerby is wholly unacquainted. I may observe that I found recent 

 shells of the first five species inhabiting the coast, a short distance to the south- 

 ward. Some shelly limestone from the same place, which Sir Woodbine 

 Parish had the kindness to show me, resembles that which I saw at Bajada, and 

 in Banda Oriental. These beds, therefore, probably form parts of the Pampas 

 deposit, and are not merely indicative of the period of its elevation. Neverthe- 

 less, on the opposite shores of the Plata, near the mouth of the Uruguay, I found 

 lines of sand dunes, where the Mactra and Cythercea Jlexuosa were lying in such 

 quantities on the bare surface, that the inhabitants, by merely sifting the sand, 

 collect them for burning into lime. 



After these facts we may feel certain, that at a period not very remote, a great 

 bay occupied the area both of the Pampas and of the lower parts of Banda 

 Oriental. Into this bay the rivers which are now united in the one great stream 

 of the Plata, must formerly have carried down (as happens at the present day) 

 the carcasses of the animals, inhabiting the surrounding countries ; and their 



