olcano appears a mass of loose
materials--a mere heap of rubbish, thrown together without the slightest
order; but on arriving at the brim of the crater, and obtaining a view
of the interior, we are agreeably surprised to discover that the
conformation of the whole displays in every part the most perfect
symmetry and arrangement. The materials are disposed in regular strata,
slightly undulating, appearing, when viewed in front, to be disposed in
horizontal planes. But, as we make the circuit of the edge of the
crater, and observe the cliffs by which it is encircled projecting or
receding in salient or retiring angles, we behold transverse sections of
the currents of lava and beds of sand and scoriae, and recognize their
true dip. We then discover that they incline outwards from the axis of
the cone, at angles varying from 30 degrees. to 40 degrees. The whole
cone, in fact, is composed of a number of concentric coatings of
alternating lavas, sand, and scoriae. Every shower of ashes which has
fallen from above, and every stream of lava descending from the lips of
the crater, have conformed to the outward surface of the hill, so that
one conical envelope may be said to have been successively folded round
another, until the aggregation of the whole mountain was completed. The
marked separation into distinct beds results from the different colors
and degrees of coarseness in the sands, scoriae, and lava, and the
alternation of these with each other. The greatest difficulty, on the
first view, is to conceive how so much regularity can be produced,
notwithstanding the unequal distribution of sand and scoriae, driven by
prevailing winds in particular eruptions, and the small breadth of each
sheet of lava as it first flows out from the crater.

But, on a closer examination, we find that the appearance of extreme
uniformity is delusive; for when a number of beds thin out gradually,
and at different points, the eye does not without difficulty recognize
the termination of any one stratum, but usually supposes it continuous
with some other, which at a short distance may lie precisely in the same
plane. The slight undulations, moreover, produced by inequalities on the
sides of the hill on which the successive layers were moulded, assist
the deception. As countless beds of sand and scoriae constitute the
greater part of the whole mass, these may sometimes mantle continuously
round the whole cone; and even lava streams may be of conside