the form in one piece,
save that there is a certain degree of flatness common to all, bears no
resemblance to the form in another. Some of the recent Astreae are of
great beauty when inhabited by the living zoophites whose skeleton
framework they compose. Every polygonal star in the mass is the house of
a separate animal, that, when withdrawn into its cell, presents the
appearance of a minute flower, somewhat like a daisy stuck flat to the
surface, and that, when stretched out, resembles a small round tower,
with a garland of leaves bound round it atop for a cornice. The _Astrea
viridis_, a coral of the tropics, presents on a ground of velvety brown
myriads of deep green florets, that ever and anon start up from the
level in their tower-like shape, contract and expand their petals, and
then, shrinking back into their cells, straightway became florets again.
The Lower Lias presented in one of its opening scenes, in this part of
the world, appearances of similar beauty widely spread. For miles
together,--we know not how many,--the bottom of a clear shallow sea was
paved with living Astreae: every irregular rock-like coral formed a
separate colony of polypora, that, when in motion, presented the
appearance of continuous masses of many-colored life, and when at rest,
the places they occupied were more thickly studded with the living
florets than the richest and most flowery piece of pasture the reader
ever saw, with its violets or its daisies. And mile beyond mile this
scene of beauty stretched on through the shallow depths of the Liasic
sea. The calcareous framework of most of the recent Astreae are white;
but in the species referred to,--the _Astrea viridis_,--it is of a
dark-brown color. It is not unworthy of remark, in connection with these
facts, that the Oolitic Astrea of Helmsdale occurs as a white, or, when
darkest, as a cream-colored petrifaction; whereas the Liasic Astrea of
Skye is invariably of a deep earthy hue. The one was probably a white,
the other a dingy-colored coral.

The Liasic bed of Astreae existed long enough here to attain a thickness
of from two to three feet. Mass rose over mass,--the living upon the
dead,--till at length, by a deposit of mingled mud and sand,--the
effect, mayhap, of some change of currents, induced we know not
how,--the innumerable polypedes of the living surface were buried up and
killed, and then, for many yards, layer after layer of a calciferous
grit was piled over them. The