cks of which the walls are composed, remains in some
places; in others a narrow channel has been cut, leaving a line of
basalt on either side. It is possible that the lava cooled faster on the
sides against the walls, and that the centre ran out; but of this we can
only conjecture. There are other places, where almost the whole of the
lava is gone, patches of it only being seen where it has caught on the
walls. As we float down, we can see that it ran out into side canons. In
some places this basalt has a fine, columnar structure, often in
concentric prisms, and masses of these concentric columns have
coalesced. In some places, where the flow occurred, the canon was
probably at about the same depth as it is now, for we can see where the
basalt has rolled out on the sands, and, what seems curious to me, the
sands are not melted or metamorphosed to any appreciable extent. In
places the bed of the river is of sandstone or limestone, in other
places of lava, showing that it has all been cut out again where the
sandstones and limestones appear; but there is a little yet left where
the bed is of lava.

What a conflict of water and fire there must have been here! Just
imagine a river of molten rock, running down into a river of melted
snow. What a seething and boiling of the waters; what clouds of steam
rolled into the heavens!

Thirty-five miles to-day. Hurrah!

_August 26._ The canon walls are steadily becoming higher as we advance.
They are still bold, and nearly vertical up to the terrace. We still see
evidence of the eruption discovered yesterday, but the thickness of the
basalt is decreasing, as we go down the stream; yet it has been
reinforced at points by streams that have come from volcanoes standing
on the terrace above, but which we cannot see from the river below.

Since we left the Colorado Chiquito, we have seen no evidences that the
tribe of Indians inhabiting the plateaus on either side ever come down
to the river; but about eleven o'clock to-day we discover an Indian
garden, at the foot of the wall on the right, just where a little
stream, with a narrow flood plain, comes down through a side canon.
Along the valley, the Indians have planted corn, using the water which
burst out in springs at the foot of the cliff for irrigation. The corn
is looking quite well, but is not sufficiently advanced to give us
roasting ears; but there are some nice green squashes. We carry ten or a
dozen of these on board our boa