Blas, may be owing to the upheaval of these latter places having been
connected with the distant line of the Cordillera, whilst that of the
provinces of La Plata was in connection with the adjoining tertiary
volcanic axis.), which may well indicate an axis of elevation quite
distinct from that of the Andes. Moreover, in the centre of the Pampas in
the chain of Cordova, severe earthquakes have been felt (See Sir W.
Parish's work on "La Plata" page 242. For a notice of an earthquake which
drained a lake near Cordova, see also Temple's "Travels in Peru." Sir W.
Parish informs me, that a town between Salta and Tucuman (north of Cordova)
was formerly utterly overthrown by an earthquake.); whereas at Mendoza, at
the eastern foot of the Cordillera, only gentle oscillations, transmitted
from the shores of the Pacific, have ever been experienced. Hence the
elevation of the Pampas may be due to several distinct axes of movement;
and we cannot judge, from the upraised shells round the estuary of the
Plata, of the breadth of the area uplifted within the recent period.

Not only has the above specified long range of coast been elevated within
the recent period, but I think it may be safely inferred from the
similarity in height of the gravel-capped plains at distant points, that
there has been a remarkable degree of equability in the elevatory process.
I may premise, that when I measured the plains, it was simply to ascertain
the heights at which shells occurred; afterwards, comparing these
measurements with some of those made during the Survey, I was struck with
their uniformity, and accordingly tabulated all those which represented the
summit-edges of plains. The extension of the 330 to 355 feet plain is very
striking, being found over a space of 500 geographical miles in a north and
south line. A table (Table 1) of the measurements is given below. The
angular measurements and all the estimations (in feet) are by the Officers
of the Survey; the barometrical ones by myself:--