they are spread over the surface, like a network of stoloniferous
roots. It is scarcely possible to set the foot on the ground
without treading on them. Both the branches and the trunks
(which stand on their roots in their natural position) are encased
in a thick, hard sheath of agglutinated sand, which has followed
the external configuration of the wood, like a cast. In some
instances the wood has entirely perished, and the envelopes are
found void like tubes, but most frequently the wood is found
within, as a distinct mass, and has become sufficiently siliceous to
scratch arragonite. V. fig. 30 and 31. The tallest fragments of trunks
reach about a foot above the surface of the sand; how far beneath it I
cannot say: there were two of these as thick as my body. Sometimes
imbedded in the envelopes of the wood, but generally in the
looser sand of the surface, were innumerable fossil-shells, intermingled
promiscuously; two species terrestrial, the third belonging
to a marine genus.
The delphinuia, fig. 33 a, b, approaches the d. sulcata of Lamarck,
only known in the fossil state, and found at Grignon. Both
helices belong to the group lamellatee of De Ferrussac’s sub-genus
helicostyla. The smaller species, fig. 32, is globose; but the larger,
fig. 34, a,b,c, (which is one inch and a quarter in its greatest
diameter, and -¡¡-ths deep) has the last whorl compressed, or
flattened. There are several helices still smaller than the former,
with the umbilicus exposed; but this is merely because the
plate which covers the columella is not entirely developed, and
I have not the least doubt of their being young shells of the
first-mentioned species. These shells are perfectly distinct from
the existing helices of Madeira, which I have already figured
or described, and there is not one to be found in this neighbourhood.
All the branches and wood appear to belong to the
same sort of tree (of which there seems to have been a small forest
on that spot), and that evidently a dicotyledon, but more than this