the level of the sea. To the westward of this bay, there is a plain
estimated at between two hundred and three hundred feet in height: this
plain seems, from many measurements, to be a continuation of the sandstone
platform of the river Negro. The next place southward, where I landed, was
at Port Desire, 340 miles distant; but from the intermediate districts I
received, through the kindness of the Officers of the Survey, especially
from Lieutenant Stokes and Mr. King, many specimens and sketches, quite
sufficient to show the general uniformity of the whole line of coast. I may
here state, that the whole of Patagonia consists of a tertiary formation,
resting on and sometimes surrounding hills of porphyry and quartz: the
surface is worn into many wide valleys and into level step-formed plains,
rising one above another, all capped by irregular beds of gravel, chiefly
composed of porphyritic rocks. This gravel formation will be separately
described at the end of the chapter.

My object in giving the following measurements of the plains, as taken by
the Officers of the Survey, is, as will hereafter be seen, to show the
remarkable equability of the recent elevatory movements. Round the southern
parts of Nuevo Gulf, as far as the River Chupat (seventy miles southward of
San Josef), there appear to be several plains, of which the best defined
are here represented.

(In the following Diagrams:
1. Baseline is Level of sea.
2. Scale is 1/20 of inch to 100 feet vertical.
3. Height is shown in feet thus:
An. M. always stands for angular or trigonometrical measurement.
Ba. M. always stands for barometrical measurement.
Est. always stands for estimation by the Officers of the Survey.