VII 
GEOLOGY OF THE PAM PA S 
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, 1 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 
1 I need hardly state here that there is good evidence against any horse living in 
America at the time of Columbus. 
