130 
TRAVELS ON THE AMAZON. 
\June, 
flowing up with great rapidity. As we proceeded down 
the river, we saw everywhere signs of its devastations in 
the uprooted trees which lined the shores all along, and 
the high mud-banks where the earth had been washed 
away. In winter, when the spring-tides are highest, the 
'' piroroco” breaks with terrific force, and often sinks and 
dashes to pieces, boats left incautiously in too shallow 
water. The ordinary explanations given of this pheno- 
menon are evidently incorrect. Here there is no meet- 
ing of salt and fresh water, neither is the stream remark- 
ably narrowed where it commences. I collected all the 
information I could respecting the depth of the river, 
and the shoals that occur in it. Where the bore first 
appears, there is a shoal across the river, and below that, 
the stream is somewhat contracted. The tide flows up 
past Para with great velocity, and entering the Guama 
river comes to the narrow part of the channel. Here 
he body of tidal water will be deeper and flow faster, 
and coming suddenly on to the shoal will form a wave, 
in the same manner that in a swift brook a large stone 
at the bottom will cause an undulation, while a slow- 
flowing stream will keep its smooth surface. This wave 
will be of great size, and, as there is a large body of 
water in motion, will be propagated onwards unbroken. 
Wherever there are shallows, either in the bed or on the 
margin of the river, it will break, or as it passes over : 
slight shoals will be increased, and, as the river narrows, 
will go on with greater rapidity. When the tides are 
low, they rise less rapidly, and at the commencement a 
much less body of water is put in motion : the depth 
of the moving water is less, and does not come in con 
