Twelve miles above Castillo we reached the mouth of the Savallo,
and stayed at a house there to breakfast, the owner, a German,
giving us roast wari, fowls, and eggs. He told me that there was a
hot spring up the Savallo, but I had not time to go and see it.
Above Savallo the San Juan is deep and sluggish, the banks low and
swampy. The large palm, so common in the delta of the river, here
reappeared with its great coarse leaves twenty feet in length,
springing from near the ground.

Our boatmen continued to paddle all day, and as night approached
redoubled their exertions, singing to the stroke of their paddles.
I was astonished at their endurance. They kept on until eleven
o'clock at night, when we reached San Carlos, having accomplished
about thirty-five miles during the day against the current. San
Carlos is at the head of the river, where it issues from the great
lake of Nicaragua, about one hundred and twenty miles from
Greytown. The mean level of the waters of the lake, according to
the survey of Colonel O.W. Childs, in 1851, is 107 1/2 feet, so
that the river falls on an average a little less than one foot per
mile. The height of the lowest pass between the lake and the
Pacific is said to be twenty-six feet above the lake, therefore at
that point the highest elevation between the two oceans is only
about 133 feet; but even allowing that an error of a few feet may
be discovered when a thorough survey is made across from sea to
sea, there can be no doubt that at this point occurs the lowest
pass between the Atlantic and the Pacific in Central America. This
fact, and the immense natural reservoir of water near the head of
the navigation, point out the route as a practicable one for a ship
canal between the two oceans.