§ 28. THE SLOTH TRIBE. 165 



1. Clay, sand, and limestone, containing marine shells 

 and shark's teeth, forming the substratum. 



2. Indurated marl. 



3. Red clayey earth with calcareous concretions and 

 bones of terrestrial animals. 



This section demonstrates that a bay of salt-water was 

 gradually encroached upon, *and at length became the bed 

 of a muddy estuary, into which floated the carcases of the 

 animals which then inhabited the neighbouring dry land. 

 It is in the upper deposits that the teeth and bones of the 

 Megatherium, Mylodon, and other gigantic animals of the 

 Sloth tribe, Armadillo, Mastodon, Horse, &c. are imbedded.* 



28. The Sloth tribe. — The most remarkable of 

 the fossil bones discovered in the Pampas, belong to 

 several extinct colossal animals of the Edentata;^ an 

 order, of which the Armadillos, Sloths, and Ant-eaters 

 are the living representatives. But as the extinct forms 

 differ greatly from the existing ones, in their gigantic pro- 

 portions, short massy extremities, and thick and strong 

 tail, their mode of life must have been very dissimilar. 

 To impart a clear perception of the peculiar modification 

 of structure which these extinct beings present, it will 

 be necessary to offer some remarks on the existing types — 

 the Sloths. 



The Sloths are arranged by naturalists in a tribe termed 

 tardigrade from their feeble power of progression on the 

 surface of the land; for the same reason they are called 

 Paresseux by the French, whence the English name, Sloth. 

 They are of slender form and small size : the largest species 

 is but little larger than a cat. They have long toes, and 

 nails which fold up, so as to enable the animal to walk, in 

 the same way as if our fingers were folded under the palms 



* Mr. Darwin, Appendix to Beechey's Voyage. 



t So named from having no teeth in the front of the jaws. 



