great difference in the nature of the pebbles at the mouth of the Santa
Cruz from those in the same latitude at the head of the valley.

I will not pretend to assign to these several and complicated agencies
their shares in the distribution of the Patagonian shingle: but from the
several considerations given in this chapter, and I may add, from the
frequency of a capping of gravel on tertiary deposits in all parts of the
world, as I have myself observed and seen stated in the works of various
authors, I cannot doubt that the power of widely dispersing gravel is an
ordinary contingent on the action of the sea; and that even in the case of
the great Patagonian shingle-bed we have no occasion to call in the aid of
debacles. I at one time imagined that perhaps an immense accumulation of
shingle had originally been collected at the foot of the Cordillera; and
that this accumulation, when upraised above the level of the sea, had been
eaten into and partially spread out (as off the present line of coast); and
that the newly-spread out bed had in its turn been upraised, eaten into,
and re-spread out; and so onwards, until the shingle, which was first
accumulated in great thickness at the foot of the Cordillera, had reached
in thinner beds its present extension. By whatever means the gravel
formation of Patagonia may have been distributed, the vastness of its area,
its thickness, its superficial position, its recent origin, and the great
degree of similarity in the nature of its pebbles, all appear to me well
deserving the attention of geologists, in relation to the origin of the
widely-spread beds of conglomerate belonging to past epochs.

FORMATION OF CLIFFS.

(DIAGRAM 7.--SECTION OF COAST-CLIFFS AND BOTTOM OF SEA, OFF THE ISLAND OF
ST. HELENA.