Oct. 1833. FOSSIL HORSE. 149 



their revolutions. At some future day this must be one of 

 the richest countries of La Plata. The soil is varied and pro- 

 ductive, and its almost insular form gives it two grand lines 

 of communication by the rivers Parana and Uruguay. 



I was delayed here five days, and employed myself in exa- 

 mining the geology of the surrounding country, which was 

 very interesting. We here see beds of sand, clay, and lime- 

 stone, containing sea-shells and sharks' teeth, passing above 

 into an indurated marl, and from that into the red clayey 

 earth of the Pampas, with its calcareous concretions and the 

 bones of terrestrial animals. This vertical section clearly 

 tells us, of a large bay of pure salt-water, gradually encroached 

 on, and at last becoming the bed of a muddy estuary, into 

 which floating carcasses were swept. I found near the Bajada 

 a large piece, nearly four feet across, of the giant armadillo- 

 like case ; also a molar tooth of a mastodon, and fragments of 

 very many bones, the greater number of which were rotten, 

 and as soft as clay. 



A tooth which I discovered by one point projecting from 

 the side of a bank, interested me much, for I at once per- 

 ceived that it had belonged to a horse. Feeling much surprise 

 at this, I carefully examined its geological position, and was 

 compelled to come to the conclusion,* that a horse, which 

 cannot from a comparison of the tooth alone, be distin- 

 guished from the existing species,t lived as a contemporary 

 with the various great monsters that formerly inhabited South 

 America. Mr. Owen and myself, at the College of Surgeons, 

 compared this tooth with a fragment of another, probably 

 belonging to the Toxodon, which was embedded at the dis- 



* The broken tooth mentioned at Bahia Blanca must not be forgotten. 



•j- As this horse existed at the same time with animals now extinct, it is 

 not probable, that it is the same species with the recent kind, although 

 from the similarity of the teeth it must have been closely allied. Cuvier, 

 talking of the remains of the horse, found fossil under similar conditions 

 in Europe, remarks, " It is not possible to say whether it was one of the 

 species now existing or not, because the skeletons of these species are so 

 like each other, that they cannot be distinguished by the mere comparison 

 ofisolated fragments." — Tlieory of the Earth, English translation, p. 283. 



