thinking that the whole of this extensive region has been at some time
or other under water, and that the present river is the drain by which
the waters have been conveyed to lower grounds. It is evident that even
now the plains (on those parts clear of trees) are frequently under
water, and that at very high floods the wooded lands are so too, for it
is almost impossible to distinguish any difference in their elevation;
but the wooded lands, from being actually higher, seem to have given
time for the growth of the diminutive timber with which they are
covered, whereas the lower plains are too frequently covered to give
time for such growth.

May 10.--The horses having strayed in the night, and it being nearly
noon before they were found, I determined to make this a halting day.

These plains are much more extensive than I supposed yesterday, and many
new plants were found on them. The river rose upwards of a foot during
the night, and still continues to rise; a circumstance which appears
very singular to me, there having been no rains of any magnitude for the
last five weeks, and none at all for the last ten days. We are also
certain that no waters fall into it or join it easterly for nearly one
hundred and fifty miles. This rise must therefore be occasioned by heavy
rains in the mountains, whence the river derives its source; but it is
not the less singular, that during its whole course, as far as it is
hitherto known, it does not receive a single tributary stream. Observed
the latitude 33. 16. 33. S.

May 11.--The river rose about four feet during the night, and still
continues to rise. Set forward on our journey down the river. About four
miles and a half from this morning's station. the river began to wash
the immediate edge of the plain, and so continued to do all along. My