1833.] ZOOLOGY OF NORTH AND SOUTH AMERICA. 123 



shells of existing species, which also proves that the period of 

 elevation of the Pampas was within the recent period. 



In the Pampsean 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 Pro- 

 fessor Owen could find in no species, either fossil or recent, a slight 

 but peculiar curvature characterizing it, until he thought of com- 

 paring it with my specimen found here: he has named this 

 American horse Equus curvidens. Certainly it is a marvellous 

 fact in the history of the Mammalia, that in South America a 

 native horse should have lived and disappeared, to be succeeded 

 in after-ages by the countless herds descended from the few intro- 

 duced with the Spanish colonists ! 



The existence in South America of a fossil horse, of the masto- 

 don, possibly of an elephant,f and of a hollow-horned ruminant, 

 discovered by MM. Lund and Clausen in the caves of Brazil, are 

 highly interesting facts with respect to the geographical distribu- 

 tion of animals. At the present time, if we divide America, not 

 by the Isthmus of Panama, but by the southern part of Mexico % 

 in lat. 20, where the great table-land presents an obstacle to the 

 migration of species, by affecting the climate, and by forming, 



* I need hardly state here that there is good evidence against any horse 

 living in America at the time of Columbus. 



t Cuvicr. Ossemens Fossiles, torn. i. p. 158. 



t This is the geographical division followed by Liclitenstein, Swainson, 

 Erichson, and Richardson. The section from Vera Cruz to Acapulco, 

 given by Humboldt in the Polit. Essay on Kingdom of N. Spain will show 

 how immense a barrier the Mexican table-land forms. Dr. Richardson, in 

 his admirable Report on the Zoology of N. America read before the Brit. 

 Assoc. 1836 (p. 157), talking of the identification of a Mexican animal 

 with the Synctheres prehensilis, says, "We do not know with what pro- 

 priety, but if correct, it is, if not a solitary instance, at least very nearly 

 so, of a rodent animal being common to North and South America." 



