The surface of the fronds is beautifully glossy; and those parts
formed where fully exposed to the light, are of a jet black colour,
but those shaded under ledges are only grey. I have shown specimens
of this incrustation to several geologists, and they all thought
that they were of volcanic or igneous origin! In its hardness and
translucency--in its polish, equal to that of the finest
oliva-shell--in the bad smell given out, and loss of colour under
the blowpipe--it shows a close similarity with living sea-shells.
Moreover in sea-shells, it is known that the parts habitually
covered and shaded by the mantle of the animal, are of a paler
colour than those fully exposed to the light, just as is the case
with this incrustation. When we remember that lime, either as a
phosphate or carbonate, enters into the composition of the hard
parts, such as bones and shells, of all living animals, it is an
interesting physiological fact to find substances harder than the
enamel of teeth, and coloured surfaces as well polished as those of
a fresh shell, re-formed through inorganic means from dead organic
matter--mocking, also, in shape, some of the lower vegetable
productions.
Pages:
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55