aggregation of this substance. I have not met with any account of similar
concretions; and considering their great toughness and compactness, their
occurrence in a bed, which probably has been subjected only to atmospheric
moisture, is remarkable.

FORMATION OF CALCAREOUS ROCKS ON THE SEA-COAST.

On several of the sea-beaches, there are immense accumulations of small,
well-rounded particles of shells and corals, of white, yellowish, and pink
colours, interspersed with a few volcanic particles. At the depth of a few
feet, these are found cemented together into stone, of which the softer
varieties are used for building; there are other varieties, both coarse and
fine-grained, too hard for this purpose: and I saw one mass divided into
even layers half an inch in thickness, which were so compact that when
struck with a hammer they rang like flint. It is believed by the
inhabitants, that the particles become united in the course of a single
year. The union is effected by calcareous matter; and in the most compact
varieties, each rounded particle of shell and volcanic rock can be
distinctly seen to be enveloped in a husk of pellucid carbonate of lime.
Extremely few perfect shells are embedded in these agglutinated masses; and
I have examined even a large fragment under a microscope, without being
able to discover the least vestige of striae or other marks of external
form: this shows how long each particle must have been rolled about, before
its turn came to be embedded and cemented. (The eggs of the turtle being
buried by the parent, sometimes become enclosed in the solid rock. Mr.
Lyell has given a figure ("Principles of Geology" book 3 chapter 17) of
some eggs, containing the bones of young turtles, found thus entombed.) One
of the most compact varieties, when placed in acid, was entirely dissolved,
with the exception of some flocculent animal matter; its specific gravity
was 2.63. The specific gravity of ordinary limestone varies from 2.6 to