414 
PHYSICAL GEOGRAPHY OE 
rent still forcing its waters onward ; but it is not easy to 
see how the stream could be thus elevated to a higher 
level than the waters of the ocean which caused the rise, 
and we should therefore suppose that at Obidos, where 
the tidal rise ceases to be felt, the river is just higher 
than the surface of the ocean at the highest spring-tides. 
A somewhat similar phenomenon is seen at the mouth 
of the Tapajoz. Here, at the end of the dry season, 
there is but a small body of water, and the current is 
very sluggish. The Amazon however rises considerably 
with the tides, and its waters then become higher than 
those of the Tapajoz, and they therefore enter into that 
river and force it back ; we then see the Amazon flow- 
ing rapidly down, at the same time th^ the Tapajoz is 
flowing up. 
It seems to be still a disputed question among geo- 
graphers, whether the Para river is or is not a branch 
of the Amazon. From my own observation, I am decid- 
edly of opinion that it is not : it appears to me to be 
merely the outlet of the Tocantins and of numerous 
other small streams. The canal or channel of Tagi- 
puru, which connects it with the Amazon, and by which 
all the trade between Para and the interior is carried on, 
is one of a complete network of channels, along which 
the tide ebbs and flows, so as in a great measure to dis- 
guise the true direction and velocity of its current. It 
seems probable that not a drop of Amazon water finds its 
way by this channel into the Para river, and I ground 
my opinion upon the following facts. 
It is well known, that in a tidal river the ebb-tide 
will continue longer than the flood, because the stream 
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