(FIGURE 12. NORTH AND SOUTH SECTION ACROSS THE VALLEY OF GUASCO, AND OF A
PLAIN NORTH OF IT.

From left (north, high) to right (south, high) through plains B and A and
the River of Guasco at the Town of Ballenar.)

On the northern side of the valley the summit-plain of gravel, A, has two
escarpments, one facing the valley, and the other a great basin-like plain,
B, which stretches for several leagues northward. This narrow plain, A,
with the double escarpment, evidently once formed a spit or promontory of
gravel, projecting into and dividing two great bays, and subsequently was
worn on both sides into steep cliffs. Whether the several escarpments in
this valley were formed during the same stationary periods with those of
Coquimbo, I will not pretend to conjecture; but if so the intervening and
subsequent elevatory movements must have been here much more energetic, for
these plains certainly stand at a much higher level than do those of
Coquimbo.

COPIAPO.

From Guasco to Copiapo, I followed the road near the foot of the
Cordillera, and therefore saw no upraised remains. At the mouth, however,
of the valley of Copiapo there is a plain, estimated by Meyen ("Reise um
die Erde" th. 1 s. 372 et seq.) between fifty and seventy feet in height,
of which the upper part consists chiefly of gravel, abounding with recent
shells, chiefly of the Concholepas, Venus Dombeyi, and Calyptraea
trochiformis. A little inland, on a plain estimated by myself at nearly
three hundred feet, the upper stratum was formed of broken shells and sand
cemented by white calcareous matter, and abounding with embedded recent
shells, of which the Mulinia Byronensis and Pecten purpuratus were the most