86 
BAHIA BLANCA 
CHAP. 
belongs to the great Pampean formation, which consists in part 
of a reddish clay, and in part of a highly calcareous marly 
rock. Nearer the coast there are some plains formed from the 
wreck of the upper plain, and from mud, gravel, and sand 
thrown up by the sea during the slo.w elevation of the land, of 
which elevation we have evidence in upraised beds of recent 
shells, and in rounded pebbles of pumice scattered over the 
country. At Punta Alta we have a section of one of these 
later-formed little plains, which is highly interesting from the 
number and extraordinary character of the remains of gigantic 
land-animals embedded in it. These have been fully described 
by Professor Owen, in the Zoology of the Voyage of the Beagle , 
and are deposited in the College of Surgeons. I will here give 
only a brief outline of their nature. 
First, parts of three heads and other bones of the Megathe¬ 
rium, the huge dimensions of which are expressed by its name. 
Secondly, the Megalonyx, a great allied animal. Thirdly, the 
Scelidotherium, also an allied animal, of which I obtained a 
nearly perfect skeleton. It must have been as large as a 
rhinoceros : in the structure of its head it comes, according to 
Mr. Owen, nearest to the Cape Ant-eater, but in some other 
respects it approaches to the armadilloes. Fourthly, the 
Mylodon Darwinii, a closely related genus of little inferior 
size. Fifthly, another gigantic edental quadruped. Sixthly, a 
large animal, with an osseous coat in compartments, very like 
that of an armadillo. Seventhly, an extinct kind of horse, to 
which I shall have again to refer. Eighthly, a tooth of a 
Pachydermatous animal, probably the same with the Macrau- 
chenia, a huge beast with a long neck like a camel, which I 
shall also refer to again. Lastly, the Toxodon, perhaps one of 
the strangest animals ever discovered : in size it equalled an 
elephant or megatherium, but the structure of its teeth, as Mr. 
Owen states, proves indisputably that it was intimately related 
to the Gnawers, the order which, at the present day, includes 
most of the smallest quadrupeds : in many details it is allied to 
the Pachydermata : judging from the position of its eyes, ears, 
and nostrils, it was probably aquatic, like the Dugong and 
Manatee, to which it is also allied. How wonderfully are the 
different Orders, at the present time so well separated, blended 
together in different points of the structure of the Toxodon ! 
