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COMMON COMPACT DOLOMITE. 99 The fracture is minute foliated, often combined with splintery, and even conclioidal. The fragments are rather bluntedged. It occurs in minute granular concretions. It is translucent. It is semi-hard ; it is harder than calcareous-spar.. It is brittle. Specific gravity of the crystals, 2.823, Tennant, 2.777, 2.820, Berger. 2.791, Thomson. 0 Chemical Characters. It dissolves slowly, and with but feeble effervescence, in nitrous acid. When deprived by heat of its carbonic acid, it is much longer of re-absorbing it from the atmo sphere than common limestone. Yorkshire. 29.5 to 31.07 Magnesia, 20.3 to 22.0.5 Carbonic Acid, 47.2 Alumina &. 5ron . 0.8 to 1.24. Tennant, Pliil. Tr. for 1799. Constituent Parts. Building Hill, near Sunderland. Carbonate of Lime, 56.80 Carbonate of Mag nesia, - 40.84 Carbonate of Iron, 0.36 Insoluble matter, 2.00 100.00 Thornton, Annals of Philosophy, vol. iv. p. 416. Humbleton Ilill, near Sunderland. Carbonate of l.ime, 51.50 Carbonate of Mag nesia, - 44,84 Insoluble matter, 1.60 Loss, - - 2.06 100.00 Thomson, ib. p. 417. Geognostic Situation. In the north of England it occurs in beds of consider ate thickness, and great extent, and appears to rest on the Newcastle coal-l'ormation * ; but in the Isle of Man, it occurs in a limestone which rests on grey-vt ackc, and G 2 contains * Thomson, Annals of Philosophy, vol. iv. p. 416,
