earth, and is scooped out by many flat-bottomed valleys. It appears to the
eye quite level, but in proceeding in a S.S.W. course, towards an
escarpment distant about six miles, and likewise ranging across the country
in a N.W. line, it was found to rise at first insensibly, and then for the
last half-mile, sensibly, close up to the base of the escarpment: at this
point it was 463 feet in height, showing a rise of 108 feet in the six
miles. On this 355-463 feet plain, I found several shells of Mytilus
Magellanicus and of a Mytilus, which Mr. Sowerby informs me is yet unnamed,
though well-known as recent on this coast; Patella deaurita; Fusus, I
believe, Magellanicus, but the specimen has been lost; and at the distance
of four miles from the coast, at the height of about four hundred feet,
there were fragments of the same Patella and of a Voluta (apparently V.
ancilla) partially embedded in the superficial sandy earth. All these
shells had the same ancient appearance with those from the foregoing
localities. As the tides along this part of the coast rise at the Syzygal
period forty feet, and therefore form a well-marked beach-line, I
particularly looked out for ridges in crossing this plain, which, as we
have seen, rises 108 feet in about six miles, but I could not see any
traces of such. The next highest plain is 710 feet above the sea; it is
very narrow, but level, and is capped with gravel; it abuts to the foot of
the 840 feet plain. This summit-plain extends as far as the eye can range,
both inland along the southern side of the valley of the Santa Cruz, and
southward along the Atlantic.

THE VALLEY OF THE R. SANTA CRUZ.

This valley runs in an east and west direction to the Cordillera, a
distance of about one hundred and sixty miles. It cuts through the great
Patagonian tertiary formation, including, in the upper half of the valley,
immense streams of basaltic lava, which as well as the softer beds, are