88 HYDROGRAPHIC REPORTS. 
2d. With regard to the capabilities of the river for navigation 
by light-draught vessels, I am satisfied that the soundings as ex- 
pressed upon the accompanying chart are reduced to the very 
lowest level to which the river ever attains. It follows, there- 
fore, that it is navigable at all seasons of the year for any vessel 
drawing less than two feet as far up as my survey reaches, and 
although it may be possible to carry that depth much higher, 
yet beyond that the bed of the river is frequently broken into 
rapids, up which no steamer of sufficiently light draught would 
have power to ascend ; and in many places it is so choked up 
with little islands as to be wholly impassable for any thing larger 
than a canoe. I therefore deem it utterly impossible to navi- 
gate the river beyond the Isla del Suchil in its present condition 
and at all seasons. In fact, the rapids at this point present an 
insuperable obstacle ; for in addition to the great fall in the bed 
of the river (some two feet in fifty — I had no means of accurate 
measurement), the channel makes nearly a right angle with 
itself, both at the head and foot of the rapids, and a steamer 
could neither ascend nor descend without risk of serious dam- 
age. Even canoes find the greatest difficulty in avoiding the 
banks in their descent. Straightening the channel would but 
increase the grade of fall, and dredging out would but remove 
the rarjids higher up. 
As appears, too, upon the chart, several rapids will be en- 
countered below this point ; but these are " rapids" only when 
the river is reduced to its lowest stage ; and even then they 
can be easily overcome by a light-draught steamer, and present 
no obstacle to an uninterrupted navigation of the river. A 
heavy rain in the upper country will cause the river to rise al- 
most immediately, and then these rapids become merely a 
strong current of some three or four knots per hour. 
In connection with this I would remark also, that this river is 
exceedingly sensitive to rains ; and I have known a heavy 
thunderstorm of three hours' duration, crossing the head- waters 
from east to west, to create a rise of two feet at the mouth of 
the Jaltepec within twenty-four hours ; which rise did not sub- 
side again for three days, and was speedily followed by another. 
And I am convinced that the minimum depth of water in the 
