122 ST. F. [CHAP. vn. 



Spaniard, who treated me with the most uncommon hospitality. 

 The Bajada is the capital of Entre Rios. In 1825 the town con- 

 tained 6000 inhabitants, and the province 30,000 ; yet, few as the 

 inhabitants are, no province has suffered more from bloody and 

 desperate revolutions. They boast here of representatives, 

 ministers, a standing army, and governors : so it is no wonder that 

 they have their revolutions. At some future day this must be one 

 of the richest countries of La Plata. The soil is varied and pro- 

 ductive ; and its almost insular form gives it two grand lines of 

 communication by the rivers Parana and Uruguay. 



I was delayed here five days, and employed myself in examining 

 the geology of the surrounding country, which was very interesting. 

 We here see at the bottom of the cliffs, beds containing sharks' 

 teeth and sea-shells of extinct species, passing above into an 

 indurated marl, and from that into the red clayey earth of the 

 Pampas, with its calcareous concretions and the bones of terrestrial 

 quadrupeds. This vertical section clearly tells us of a large bay of 

 pure salt-water, gradually encroached on, and at last converted 

 into the bed of a muddy estuary, into which floating carcasses were 

 swept. At Punta Gorda, in Banda Oriental, I found an alternation 

 of the Pamprean estuary deposit, with a limestone containing some 

 of the same extinct sea-shells ; and this shows either a change in 

 the former currents, or more probably an oscillation of level in the 

 bottom of the ancient estuary. Until lately, my reasons for con- 

 sidering the Pampaean formation to be an estuary deposit were, its 

 general appearance, its position at the mouth of the existing great 

 river the Plata, and the presence of so many bones of terrestrial 

 quadrupeds : but now Professor Ehrenberg has had the kindness 

 to examine for me a little of the red earth, taken from low down in 

 the deposit, close to the skeletons of the mastodon, and he finds in 

 it many infusoria, partly salt-water and partly fresh-water forms, 

 with the latter rather preponderating; and therefore, as he 

 remarks, the water must have been brackish. M. A. d'Orbigny 

 found on the banks of the Parana, at the height of a hundred feet, 

 great beds of an estuary shell, now living a hundred miles lower 

 down nearer the sea; and I found similar shells at a less height on 

 the banks of the Uruguay : this shows that just before the Pampas 

 was slowly elevated into dry land, the water covering it was 

 brackish. Below Buenos Ayres there are upraised beds of sea- 



