Llandillo rocks, (darkish calcareous flagstones;) 2 and 3, two groups
called Caradoc rocks; 4, Wenlock shale; 5, Wenlock limestone; 6,
Lower Ludlow rocks, (shales and limestones;) 7, Aymestry limestone;
8, Upper Ludlow rocks, (shales and limestone, chiefly micaceous.)
From the lowest beds upwards, there are polypiaria, though most
prevalent in the Wenlock limestone; conchifera, a vast number of
genera, but all of the order brachiopoda, (including terebratula,
pentamerus, spirifer, orthis, leptaena;) mollusca, of several orders
and many genera, (including turritella, orthoceras, nautilus,
bellerophon;) crustacea, all of them trilobites, (including
trinucleus, asaphus, calamene.) A little above the Llandillo rocks,
there have been discovered certain convoluted forms, which are now
established as annelids, or sea-worms, a tribe of creatures still
existing, (nereidina and serpulina,) and which may often be found
beneath stones on a sea-beach. One of these, figured by Mr.
Murchison, is furnished with feet in vast numbers all along its body,
like a centipede. The occurrence of annelids is important, on
account of their character and status in the animal kingdom. They
are red-blooded and hermaphrodite, and form a link of connexion
between the annulosa (white-blooded worms) and a humble class of the
vertebrata. {62} The Wenlock limestone is most remarkable amongst
all the rocks of the Silurian system, for organic remains. Many
slabs of it are wholly composed of corals, shells, and trilobites,
held together by shale. It contains many genera of crinoidea and
polypiaria, and it is thought that some beds of it are wholly the
production of the latter creatures, or are, in other words, coral
reefs transformed by heat and pressure into rocks. Remains of
fishes, of a very minute size, have been detected by Mr. Philips in
the Aymestry limestone, being apparently the first examples of
vertebrated animals which breathed upon our planet. In the upper