GEOLOGY OF THE PAMPAS. 1G5 



were svvcjit. At Punta Gorda, in Banda Oncntal, 

 I found an alternation of the Pamptean estuary- 

 deposit, with a limestone containing; some of the 

 same extinct sea-shells ; and this shows either a 

 change in the former currents, or more probably 

 an oscillation of level in the bottom of the ancient 

 estuary. Until lately, my reasons for considering 

 the Pampaean formation to be an estuary deposit 

 were, its general appearance, its position at the 

 mouth of the existing great river the Plata, and 

 the presence of so many bones of terrestrial quad- 

 rupeds ; but now Professor Ehrenberg has had 

 the kindness to examine for me a little of the red 

 earth, taken from low down in the deposit, close to 

 the skeletons of the mastodon, and he finds in it 

 many infusoria, partly salt-water and partly fresh- 

 water forms, with the latter rather preponderating ; 

 and thei'efore, as he remarks, the water must have 

 been brackish. M. A. d'Orbigny found on the 

 banks of the Parana, at the height of a hundred 

 feet, great beds of an estuary shell, now living a 

 hundred 7Tiiles lower down nearer the sea ; and I 

 found similar shells at a less height on the banks of 

 the Uruguay : this shows that just before the Pam- 

 pas was slowly elevated into dry land, the water 

 covering it was brackish. Below Buenos Ayres 

 there are upraised beds of sea-shells of existing 

 species, which also proves that the period of eleva- 

 tion of the Pampas was within the recent period. 



In the Pampeean deposit at the Bajada I found 

 the osseous armour of a gigantic armadillo-like an- 

 imal, the inside of which, when the earth was re- 

 moved, was like a great cauldron ; I found also 

 teeth of the Toxodon and Mastodon, and one tooth 

 of a Horse, in the same stained and decayed state. 

 This latter tooth gi-eatly interested me,* and I took 



* I need hardly state here that there is good evidence against 

 any horse living in America at the time of Columbua. 



