458 Reviews — Agassiz's Journey in Brazil. 



lined with a Cretaceous deposit, which crops out at various localities 

 along its borders. It is thus a Cretaceous basin. Of the Tertiary 

 period there is no representative known, as the succeeding formations 

 are of later date. These are three in number, the oldest of which 

 is rarely visible, but consists of sandstone or stratified sand; upon 

 this rests everywhere an extensive deposit of finely-laminated clays 

 (sometimes looking like clay-slates), which have yielded fossil leaves 

 closely resembling those of plants living in the region. The second 

 formation, (formerly referred either to the Old Eed or the Trias,) 

 consists of beds of sand and sandstone, frequently false-bedded, 

 presenting a variety of aspects, and being very variable in thickness : 

 in some places forming isolated hills 800 feet in height, and in 

 others being represented by a mere remnant. The third and upper- 

 most deposit is clayey, containing more or less sand, and reddish 

 in colour. In the upper portion of the valley it is obscurely strati- 

 fied, and its materials are small ; but near Rio, it contains large 

 stones. Almost everywhere its base is marked by a bed of small 

 pebbles, and it reposes unconformably on the underlying formation. 

 Professor Agassiz, however, has convinced himself that they were 

 deposited by the same water-system within the same basin, but at 

 different levels. 



The extent of these formations is something marvellous, but so is 

 the explanation of their origin. 



Professor Agassiz believes that all these deposits belong to the 

 ice-period in its earlier or later phases. He infers that the valley of 

 the Amazon had an enormous glacier poured down into it from 

 the accumulations of snow in the Cordilleras, and swollen laterally 

 by the tributary glaciers descending from the table-lands of Guiana 

 and Brazil. Its movement was eastward, it ploughed up and 

 ground down the bottom of the valley, and it built up as its terminal 

 moraine a colossal sea-wall of gigantic proportions. But there are 

 no furrows, no stride, no polishing. Professor Agassiz replies, 

 because there are no natural rock-surfaces ; and there are rocJies 

 moutonnees and boulders. The climate then became milder, and the 

 glacier partially melted, transforming the basin with its sea-wall 

 into a vast fresh-water lake, covered with a thick crust of ice. 

 Under these circumstances were deposited the coarse pebbly sand 

 and the superposed finely laminated clays. Our author expects to 

 be here reminded of his fossil leaves and their tropical character, and 

 he makes a very poor reply, — for the vegetation of Switzerland, on 

 the borders of glaciers, to which he appeals, is certainly not tropical. 



The second formation belongs to a later period, when the whole 

 body of ice being more or less thawed, the basin contained a larger 

 quantity of water ; and we are asked to believe that under these cir- 

 cumstances a sandstone formation was deposited, here and there 

 false-bedded, and attaining a thickness of 800 feet. At the end of 

 this time, the sea is supposed to have worn away the terminal moraine 

 so as to release this vast body of -water, which consequently rushed 

 violently seaward, denuding the sandstone it had just deposited, 

 except in a few places where it left the flat-topped " denudation 



