70 
THE AMAZON AND MADEIRA RIVERS. 
Two and a half miles above Ribeirao is the strait known under the 
name of Coreenteza da Miseeicoedia ; the total width of the river being 
naiTowed here to 382 yards. As the steep, rocky shores do not allow 
of an extension of the floods on cither side, and as the whole enormous 
mass of water must pass tlirough the nan-ow, and not very deep, opening, 
the water is necessarily volumed hero, and its rapidity is considerably 
increased. 
Thus, while the height of the falls is generally less at high water, 
it increases in the same proportion in the straits, where the overflow 
is cheeked by the limiting ridges. 
As there is, besides, a sharp bend in the river, rendci’ing the tracldng 
from the shore extremely difficult, the CoiTcnteza da Misericordia must, 
indeed, at certain times, be an anxious spot for the Bolivian barques. 
When we passed there, on the 15th of August, the river was low, and 
Ave experienced no difficulty in coming up against the current. Above 
Misericordia the Madeira again reaches its normal breadth of 7G0 to 880 
yai'ds, and is as smooth as a lake up to the Cachoeira da Madeira. 
Just below this it widens to almost 2,200 yards, and is divided by 
two isles into thi'ee main channels. 
The Cachoeira, or rapid, itself, is a chaos of small flat islets and 
reefs, between Avhich the waiter rushes with a total declivity of 9 feet 
10 inches. We wane again compelled to unload here, and to carry the 
cargo on land till above the rapid. 
On the metamorphic rocks of the shore we found couccutrie chcles, 
like those at the Caldeirao ; but the most striking feature of the 
Cachoeira da Madeira is the enormous quantity of drift-wmod deposited 
on the rocks of the left shore, directly below the mouth of the Beni. 
Huge trunks of the cedar, and other giants of the forest, swept 
doAvu by the floods of the Beni, and driven by currents and eddies 
amongst the rocks, have stranded there wdth the fall of the river; 
and there they Avill remain until, pei'haps, next year’s flood may 
carry them away down-stream. Those entangled masses of many 
hundreds of colossal trunks have doubtless induced the Portuguese to 
give the name of Madeira (timber, wood) to this rapid ; and the enormous 
canons of the Colorado and its affluents, where the effects of erosion are striking’ 
indeed. The Colorado ha,s hoUowed for itself, out of very hard stone, a bed, the 
A'ei-tical walls of which reach the enormous height of o,000 feet in several places ; 
once even 7,000 feet. The ravine extends for more than 500 English miles. 
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