Note 55 — SECTION II. PHYSICAL GEOGRAPHY OF ICELAND.
Reading edition
About ninety species of mollusk shells and the hard parts of echinoderms and crustaceæ have been found in the Palagonite of Sicilian Aci Castello. Lime, for the use of the shell-builders, enters into the composition of such tuffs generally, and the percentage depends upon the percentage of shells. Silica is extracted from it by carbonic acid and sulphuretted hydrogen; and this mineral again depends upon the included quantity of infusorial skeletons. Professor Quekett, Dr Gulliver, and other authorities, have examined specimens of Icelandic Palagonite, in which they could not detect infusoria nor their skeletons, even after boiling in nitric acid.