chapter that remains thus exposed in time decay and disappear.

(FIGURE 13. SECTION OF THE PLAIN AT THE EASTERN FOOT OF THE CHILEAN
CORDILLERA.

From Cordillera (left) through Talus-plain and Level surface, 2,700 feet
above sea, to Gravel terraces (right).)

I observed some appearances on the plains at the eastern and opposite foot
of the Cordillera which are worth notice, as showing that the sea there
long acted at nearly the same level as on the basin-plains of Chile. The
mountains on this eastern side are exceedingly abrupt; they rise out of a
smooth, talus-like, very gentle, slope, from five to ten miles in width (as
represented in Figure 13), entirely composed of perfectly rounded pebbles,
often white-washed with an aluminous substance like decomposed feldspar.
This sloping plain or talus blends into a perfectly flat space a few miles
in width, composed of reddish impure clay, with small calcareous
concretions as in the Pampean deposit,--of fine white sand with small
pebbles in layers,--and of the above-mentioned white aluminous earth, all
interstratified together. This flat space runs as far as Mendoza, thirty
miles northward, and stands probably at about the same height, namely,
2,700 feet (Pentland and Miers) above the sea. To the east it is bounded by
an escarpment, eighty feet in height, running for many miles north and
south, and composed of perfectly round pebbles, and loose, white-washed, or
embedded in the aluminous earth: behind this escarpment there is a second
and similar one of gravel. Northward of Mendoza, these escarpments become
broken and quite obliterated; and it does not appear that they ever
enclosed a lake-like area: I conclude, therefore, that they were formed by
the sea, when it reached the foot of the Cordillera, like the similar
escarpments occurring at so many points on the coasts of Chile and