210 Miscellanies. 
from the development of the nasal cavity, and the frontal sinus, that 
it is extremely improbable the habits of the species were so strictly 
aquatic as the entire absence of hinder extremities would occasion. 
In conclusion, he pointed out the interesting fact, that the recent 
animal most analogous to the Toxodon, combining the characters of 
a Pachyderm and a Rodent, and, from its aquatic habits, called the’ 
Water-hog, or Hydrocherus, exists only in South America; the same 
region in which this gigantic fossil, possessing similar aberrant pecu- 
liarities, has been discovered. 
May 3.—Rev. W. Whewell, President, in the chair. 
The first paper read was one by Mr. Darwin, describing the dis- 
trict in which had been found the remains of the Toxodon, described 
at the last meeting by Mr. Owen. ‘The countries bordering the 
Rio de Ja Plata contain, in great numbers, the remains of extinct 
animals. ‘The province of Bander Oriental consists of granite, and 
other primary rocks. The flat and extensive plains of the Pampas 
‘are very uniform in structure over a very extensive tract. A red- 
dish argillaceous earth covers the surface, with irregular concretions 
of an aluminous limestone, or indurated marl, which sometimes unite 
and form a stratum, often replacing the former, both containing oc- 
casional layers of crystallized sulphate of lime. In the province of 
Entre Rios, these rest on strata consisting of sand, layers of clay, 
and a fine white crystalline limestone, containing shark’s teeth, Arca 
Venus, and Pecten, all resembling recent shells: But it is m the 
superincumbent deposit that are found the fossil Mammalia, peculiar 
to this district, consisting besides the Toxodon, Megatherium, a lesser 
animal, protected by an armadillo-like covering, Mastodon, another 
singular animal, of which only half the head has been preserved, and, 
as Mr. Darwin believes, also the horse. 
In several places Mr. Darwin observed clear proofs of a change 
of the level between land and water. ‘These he considers connected 
with the greater changes on the opposite coast, and concludes that, 
within a period geologically recent, a great bay occupied the area 
both of the Pampas and the low parts of Bander Oriental. Into 
this the river poured, as in the present day, reddish sediment from 
the decomposition of the granites of Brazil, and charged lime with 
gypsum, perhaps, from the Cordilleras. ‘The bodies of the animals, 
which formerly inhabited the surrounding country, must have been 
_ likewise swept into this bay, which has now been elevated into dry 
land. 
