capped by gravel; and this gravel, high up the river, is associated with a
vast boulder formation. (I have described this formation in a paper in the
"Geological Transactions" volume 6 page 415.) In ascending the valley, the
plain which at the mouth on the southern side is 355 feet high, is seen to
trend towards the corresponding plain on the northern side, so that their
escarpments appear like the shores of a former estuary, larger than the
existing one: the escarpments, also, of the 840 feet summit-plain (with a
corresponding northern one, which is met with some way up the valley),
appear like the shores of a still larger estuary. Farther up the valley,
the sides are bounded throughout its entire length by level, gravel-capped
terraces, rising above each other in steps. The width between the upper
escarpments is on an average between seven and ten miles; in one spot,
however, where cutting through the basaltic lava, it was only one mile and
a half. Between the escarpments of the second highest terrace the average
width is about four or five miles. The bottom of the valley, at the
distance of 110 miles from its mouth, begins sensibly to expand, and soon
forms a considerable plain, 440 feet above the level of the sea, through
which the river flows in a gut from twenty to forty feet in depth. I here
found, at a point 140 miles from the Atlantic, and seventy miles from the
nearest creek of the Pacific, at the height of 410 feet, a very old and
worn shell of Patella deaurita. Lower down the valley, 105 miles from the
Atlantic (longitude 71 degrees W.), and at an elevation of about 300 feet,
I also found, in the bed of the river, two much worn and broken shells of
the Voluta ancilla, still retaining traces of their colours; and one of the
Patella deaurita. It appeared that these shells had been washed from the
banks into the river; considering the distance from the sea, the desert and
absolutely unfrequented character of the country, and the very ancient
appearance of the shells (exactly like those found on the plains nearer the
coast), there is, I think, no cause to suspect that they could have been
brought here by Indians.