NOTE XIX … FLINT.
1. Siliceous rocks from morasses; their cements. 2. Siliceous trees; coloured by iron or manganese; Peak-diamonds; Bristol-stones; flint in form of calcareous spar; has been fluid without much heat; obtained from powdered quartz and fluor-acid by Bergman and by Achard. 3. Agates and onyxes found in sand-rocks; of vegetable origin; have been in complete fusion; their concentric coloured circles not from superinduction but from congelation; experiment of freezing a solution of blue vitriol; iron and manganese repelled in spheres as the nodule of flint cooled; circular stains of marl in salt-mines; some flint nodules resemble knots of wood or roots. 4. Sand of the sea; its acid from morasses; its base from shells. 5. Chert or petrosilex stratified in cooling; their colour and their acid from sea-animals; labradore-stone from mother- pearl. 6. Flints in chalk-beds; their form, colour, and acid, from the flesh of sea-animals; some are hollow and lined with crystals; contain iron; not produced by injection from without; coralloids converted to flint; French-millstones; flints sometimes found in solid strata. 7. Angles of sand destroyed by attrition and solution in steam; siliceous breccia cemented by solution in red-hot water. 8. Basaltes and granites are antient lavas; basaltes raised by its congelation not by subterraneous fire.