hores of the bay,--a crag of a
singularly rough appearance, that projects mole-like from the sward upon
the beach, and then descending abruptly to the level of the other
strata, runs out in a long ragged line into the sea. The stratum, from
two to three feet in thickness, of which it is formed, seems wholly
built up of irregularly-formed rubbly concretions, just as some of the
garden-walls in the neighborhood of Edinburgh are built of the rough
scoria of our glass-houses; and we find, on examination, that every
seeming concretion in the bed is a perfectly formed coral of the genus
Astrea. We have arrived at an entire bed of corals, all of one species.
Their surfaces, wherever they have been washed by the sea, are of great
beauty: nothing can be more irregular than the outline of each mass, and
yet scarce anything more regular than the sculpturings on every part of
it. We find them fretted over with polygons, like those of a honeycomb,
only somewhat less mathematically exact, and the centre of every polygon
contains its many-rayed star. It is difficult to distinguish between
species in some of the divisions of corals: one Astrea, recent or
extinct, is sometimes found so exceedingly like another of some very
different formation or period, that the more modern might almost be
deemed a lineal descendant of the more ancient species. With an eye to
the fact, I brought with me some characteristic specimens of this
Astrea[4] of the Lower Lias, which I have ranged side by side with the
Astreae of the Oolite I had found so abundant a twelvemonth before in the
neighborhood of Helmsdale. In some of the hand specimens, that present
merely a piece of polygonal surface, bounded by fractured sides, the
difference is not easily distinguishable: the polygonal depressions are
generally smaller in the Oolitic species, and shallower in the Liasic
one; but not unfrequently these differences disappear, and it is only
when compared in the entire unbroken coral that their specific
peculiarities acquire the necessary prominence. The Oolitic Astrea is of
much greater size than the Liasic one: it occurs not unfrequently in
masses of from two to three feet in diameter; and as its polygons are
tubes that converge to the footstalk on which it originally formed, it
presents in the average outline a fungous-like appearance; whereas in
the smaller Liasic coral, which rarely exceeds a foot in diameter, there
is no such general convergency of the tubes; and