ElVEES OF AMAZONIA. 



99 



doubt tliat at some remote period the whole region of plains and terraces formed 

 the bed of a vast lake, or of several lakes constituting an American Mediterranean 

 larger than the Canadian lake system, larger even than the Mediterranean of the 

 Old World. In the Pebas cliffs on the Peruvian Maranon, Orton discovered, 

 embedded in layers of many-coloured clays, a mass of marine shells comprising no 

 less than 17 extinct species dating from the close of the Tertiary epoch. 



At that time the Maranon, issuing from the Manseriche gorges, entered the 

 inland sea through a delta, which, gradually advancing eastwards, at last filled 

 the whole plain. Possibly the fluvial waters were then discharged north-eastwards 

 in the direction of the Caribbean Sea through the depression at present traversed 



Fig. 33. — AMAzoMiN Depression and Outer Zone of the Cataracts. 

 Scale 1 : 36,000,OiX>. 



Zone of the Amazons Affluents above the Falls. 



1,250 Miles. 



by the Ptio Negro, the Cassiquiare, and the Orinoco. At least the marine shells 

 of the Upper Amazons resemble the types characteristic of the West Indian 

 waters. In that case, the bluffs of Monte Alegre, the Santarem heights, and 

 the other hills approaching the banks of the Amazons at the Obidos narrows, 

 should be regarded as the remains of the ridge or dyke which formerly closed the 

 basin of the inland sea and of the lakes ascending in terraces up the slopes of the 

 Andes to Lake Titicaca. 



The Amazonian Floods. 

 As regular in its periodical changes as the Nile itself, the Amazons rises and 

 falls with the alternating seasons by a succession of " ebbs " and "■ flows " 

 {(Vichente and vasante), in which the inhabitants recognise a sort of tidal move- 



