are extinct. The number of species which certainly belong to existing
kinds, although few in number, are sufficient to show that the deposit
belongs to a late tertiary period. From its mineralogical character, from
the number and size of the embedded fragments, and from the abundance of
Patellae, and other littoral shells, it is evident that the whole was
accumulated in a shallow sea, near an ancient coast-line.

EFFECTS PRODUCED BY THE FLOWING OF THE SUPERINCUMBENT BASALTIC LAVA OVER
THE CALCAREOUS DEPOSIT.

These effects are very curious. The calcareous matter is altered to the
depth of about a foot beneath the line of junction; and a most perfect
gradation can be traced, from loosely aggregated, small, particles of
shells, corallines, and Nulliporae, into a rock, in which not a trace of
mechanical origin can be discovered, even with a microscope. Where the
metamorphic change has been greatest, two varieties occur. The first is a
hard, compact, white, fine-grained rock, striped with a few parallel lines
of black volcanic particles, and resembling a sandstone, but which, upon
close examination, is seen to be crystallised throughout, with the
cleavages so perfect that they can be readily measured by the reflecting
goniometer. In specimens, where the change has been less complete, when
moistened and examined under a strong lens, the most interesting gradation
can be traced, some of the rounded particles retaining their proper forms,
and others insensibly melting into the granulo-crystalline paste. The
weathered surface of this stone, as is so frequently the case with ordinary
limestones, assumes a brick-red colour.

The second metamorphosed variety is likewise a hard rock, but without any
crystalline structure. It consists of a white, opaque, compact, calcareous
stone, thickly mottled with rounded, though regular, spots of a soft,