432 A JOURNEY IN BRAZIL. 
longitudinal channel of the Amazons itself, but also the 
lateral furrows through which its tributaries reach the 
main stream, and the network of anastomosing branches 
flowing between them ; the whole forming the most ex 
traordinary river system in the world. 
My assumption that the sea has produced very extensive 
changes in the coast of Brazil changes more than suffi- 
cient to account for the disappearance of the glacial wall 
which I suppose to have closed the Amazonian Valley in the 
ice period- -is by no means hypothetical. This action is 
still going on to a remarkable degree, and is even now rapid- 
ly modifying the outline of the shore. When I first arrived 
at Para, I was struck with the fact that the Amazons, the 
largest river in the world, has no delta. All the other riv- 
ers which we call great, though some of them are insignifi- 
cant as compared with the Amazons, the Mississippi, 
the Nile, the Ganges, and the Danube, deposit extensive 
deltas, and the smaller rivers also, with few exceptions, are 
constantly building up the land at their mouths by the ma- 
terials they bring along with them. Even the little river 
Kander, emptying into the lake of Thtm, is not without its 
delta. Since my return from the Upper Amazons to Par&, 
I have made an examination of some of the harbor islands, 
and also of parts of the coast, and have satisfied myself that, 
with the exception of a few small, low islands, never rising 
above the sea-level, and composed of alluvial deposit, they 
are portions of the main-land detached from it, partly by the 
action of the river itself, and partly by the encroachment of 
the ocean. In fact, the sea is eating away the land much 
faster than the river can build it up. The great island of 
Marajo was originally a continuation of the valley of the 
Amazons, and is identical with it in every detail of its geo- 
