with the upper step-like plain F, there cannot, I apprehend, be any doubt,
that these six terraces have been formed by the action of the sea; and that
their five escarpments mark so many periods of comparative rest in the
elevatory movement, during which the sea wore into the land. The elevation
between these periods may have been sudden and on AN AVERAGE not more than
seventy-two feet each time, or it may have been gradual and insensibly
slow. From the shells on the three lower terraces, and on the upper one,
and I may add on the three gravel-capped terraces at Conchalee, being all
littoral and sub-littoral species, and from the analogical facts given at
Valparaiso, and lastly from the evidence of a slow rising lately or still
in progress here, it appears to me far more probable that the movement has
been slow. The existence of these successive escarpments, or old cliff-
lines, is in another respect highly instructive, for they show periods of
comparative rest in the elevatory movement, and of denudation, which would
never even have been suspected from a close examination of many miles of
coast southward of Coquimbo.

(FIGURE 10. NORTH AND SOUTH SECTION ACROSS THE VALLEY OF COQUIMBO.

From north F (high) through E?, D, C, B, A (low), B?, C, D?, E, F (high).

Vertical scale 1/10 of inch to 100 feet: horizontal scale much contracted.

Terraces marked with ? do not occur on that side of the valley, and are
introduced only to make the diagram more intelligible. A river and bottom-
plain of valley C, E, and F, on the south side of valley, are respectively,
197, 377, and 420 feet above the level of the sea.

AA. The bottom of the valley, believed to be 100 feet above the sea: it is
continuously united with the lowest plain A of Figure 9.