Itf SOUTH AMERICA. 109 



earth of the Pampas at Bojada de Santa Fe, in the 

 Province of Entre Eios. This tooth agreed so closely 

 in color and condition with the remains of the masto- 

 don and toxodon, from the same locality, that I have 

 no doubt respecting the contemporaneous existence of 

 the individual horse of which it once formed part. 

 This tooth is figured at Plate xxxii, Figs. 13 and 14, 

 from which the anatomist can judge of its close corre- 

 spondence with a middle molar of the left side of the 

 upper jaw. 



u This evidence of the former existence of a genus 

 which, as regards South America, had become extinct, 

 and has a second time been introduced into that conti. 

 nent, is not one of the least interesting points of Mr. 

 Darwin's paleontological discoveries." * 



* Mr. Darwin, in his work on " The Descent of Man " (vol. i, 

 pp. 280-1), says : " Although the gradual decrease and final ex- 

 tinction of the races of man is an obscure problem, we can see 

 that it depends on many causes, differing in different places and 

 at different times. It is the same difficult problem as that pre- 

 sented by the extinction of one of the higher animals of the 

 fossil horse, for instance which disappeared from South Amer- 

 ica, soon to be replaced, within the same districts, by countless 

 herds of the Spanish horse." 



In his "Journal of Researches" (pp. 130-1-2), Mr. Darwin 

 gives further information concerning the fossil teeth described 

 by Prof. Owen, and advances a theory of the introduction of the 

 horse into the " so-called New World." He says : " In the Pam- 

 paean deposit of the Bojada I found the osseous armor of a gigan- 

 tic, armadillo-like animal, the inside of which, when the earth 

 was removed, was like a great cauldron. I also found teeth of 

 the toxodon and mastodon, and one of a horse, in the same 

 stained and decayed state. The latter greatly interested me, and 

 I took scrupulous care in ascertaining that it had been im- 

 bedded contemporaneously with the other remains ; for I was 

 not then aware that among the fossils from Bahia Blanca there 



