60 BAHIA BLANCA. [CHAP. V. 



eight fresh-water and one salt-water infusorial animalcule; therefore, 

 probably, it was an estuary deposit. 



The remains at Punta Alta were embedded in stratified gravel and 

 reddish mud, just such as the sea might now wash up on a shallow bank. 

 They were associated with twenty-three species of shells, of which 

 thirteen are recent and four others very closely related to recent forms ; 

 whether the remaining ones are extinct or simply unknown, must be 

 doubtful, as few collections of shells have been made on this coast. As, 

 however, the recent species were embedded in nearly the same propor- 

 tional numbers with those now living in the bay, I think there can be 

 little doubt, that this accumulation belongs to a very late tertiary period. 

 From the bones of the Scelidotherium, including even the knee-cap, 

 being intombed in their proper relative positions, and from the osseous 

 armour of the great armadillo-like animal being so well preserved, 

 together with the bones of one of its legs, we may feel assured that 

 these remains were fresh and united by their ligaments, when deposited 

 in the gravel together with the shells. Hence we have good evidence 

 that the above enumerated gigantic quadrupeds, more different from 

 those of the present day than the oldest of the tertiary quadrupeds of 

 Europe, lived whilst the sea was peopled with most of its present 

 inhabitants ; and we have confirmed that remarkable law so often 

 insisted on by Mr. Lyell, namely, that the " longevity of the species in 

 the mammalia is upon the whole inferior to that of the testacea."* 



The great size of the bones of the Megatheroid animals, including 

 the Megatherium, Megalonyx, Scelidotherium, and Mylodon, is truly 

 wonderful. The habits of life of these animals were a complete puzzle 

 to naturalists, until Professor Owenf lately solved the problem with 

 remarkable ingenuity. The teeth indicate, by their simple structure, that 

 these Megatheroid animals lived on vegetable food, and probably on the 

 leaves and small twigs of trees ; their ponderous forms and great strong 

 curved claws seem so little adapted for locomotion, that some eminent 

 naturalists have actually believed, that, like the sloths, to which they are 

 intimately related, they subsisted by climbing back down wards on trees, 

 and feeding on the leaves. It was a bold, not to say preposterous, idea 

 to conceive even antediluvian trees, with branches strong enough to 

 bear animals as large as elephants. Professor Owen, with far more 

 probability, believes that, instead of climbing on the trees, they pulled the 

 branches down to them, and tore up the smaller ones by the roots, and 

 so fed on the leaves. The colossal breadth and weight of their hinder 

 quarters, which can hardly be imagined without having been seen, 

 become, on this view, of obvious service, instead of being an encum- 

 brance ; their apparent clumsiness disappears. With their great tails 

 and their huge heels firmly fixed like a tripod on the ground, they could 

 freely exert the full force of their most powerful arms and great claws. 

 Strongly rooted, indeed, must that tree have been, which could have 

 resisted such force 1 The Mylodon, moreover, was furnished with a 



* "Principles of Geology," vol. iv., p. 40. 



f This theory was first developed in the Zoology of the Voyage of the 

 Beagle, and subsequently in Professor Owen's Memoir on Mylodon robustus. 



