y 



8 



ZOOLOGY OF THE VOYAGE OF THE BEAGLE. 



the time of their burial, must have been deeper than at present. This conclusion 

 might also have been inferred from the fact, that in the neighbouring cliff the same 

 bed, with its shells, has been uplifted some yards above high- water mark. On 

 the coast to the southward abundant proofs occur, of a recent elevation of the con- 

 tinent. In the gravel, nearly all the pebbles are of quartz, and have originally 

 proceeded from the lofty range of the Ventana, distant between forty and fifty 

 miles. Besides the pebbles of quartz, there are a few irregular masses of the 

 same indurated marl, of which the escarpment of the neighbouring great plain is 

 composed. Hence the gravel beds must have been deposited, when the plain ex- 

 isted as dry land ; and on it probably those great animals once lived, of which 





we now find only the remains. The indurated marl forming the plain, is the same 

 kind of rock with that occurring over a wide extent of the Pampas ; and there 

 is no reason to doubt, they are parts of one great formation. Nevertheless, the 

 gravel bed of Bahia Blanca, although subsequent to the calcareous formation, 

 may be of the same age with those parts of the Pampas, which stand at a low 

 level near the Plata. For on this whole line of coast, I believe, as the land 

 has continued rising, fresh littoral deposits have been formed ; and each of 

 these would often owe part of its materials to the degradation of the one last 



elevated. 



t 



With respect to the relative age of the Monte Hermoso and Punta Alta beds, 

 it is not possible to speak decidedly. A certain degree of similarity in the 

 nature of the strata containing quartz pebbles, and those of the reddish in- 

 durated earth; and the short distance between the two localities, would indicate 

 that no long interval had intervened. The beds at Monte Hermoso, certainly 

 were deposited more tranquilly, and probably in a deeper sea; so that even 

 skeletons of animals, no larger than rats, have been perfectly preserved there. 

 In some parts of the surrounding country, obscure traces of a succession of step- 

 formed terraces may be observed ; and each of these indicates a period of repose 

 during the elevation of the land, at which time the strata previously existing were 

 worn away, and fresh matter deposited. The Monte Hermoso beds were, per- 

 haps, formed during one such interval, anterior to the accumulation of the shingle 

 bank at Punta Alta. 



