VII GEOLOGY OF THE PAMPAS 137 



Oriental, I found an alternation of the Pampaean 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 quadrupeds : 

 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 therefore, 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 miles 

 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 Pampas 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 elevation of the Pampas was within the 

 recent period. 



In the Pampaean deposit at the Bajada I found the osseous 

 armour of a gigantic armadillo-like animal, the inside of which, 

 when the earth was removed, 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 greatly interested me,^ and I took scrupulous care in 

 ascertaining that it had been embedded contemporaneously with 

 the other remains ; for I was not then aware that amongst the 

 fossils from Bahia Blanca there was a horse's tooth hidden in 

 the matrix : nor was it then known with certainty that the 

 remains of horses are common in North America. Mr. Lyell 

 has lately brought from the United States a tooth of a horse ; 

 and it is an interesting fact, that Professor Owen could find in 

 no species, either fossil or recent, a slight but peculiar curvature 

 characterising it, until he thought of comparing it with my 



^ I need hardly state here that there is good evidence against any horse living in 

 America at the time of Columbus. 



