The microscope and its revelations . ted amongMicroscopists for the number and beauty of the forms theyhave yielded; the former constitutes a stratum of 18 feet inthickness, underlying the whole city, and extending over anarea whose limits are not known. Several deposits of morelimited extent, and apparently of fresh-water origin, havebeen found in our own islands; as for instance at DolgeUy inNorth Wales, at Lough Mourne in Ireland (Fig. 102j, andin the island of MuU in Scotland. Similar deposits in Swedenand Norway are known under the name of berg-meld ormountain-flour; and in times of scarc
The microscope and its revelations . ted amongMicroscopists for the number and beauty of the forms theyhave yielded; the former constitutes a stratum of 18 feet inthickness, underlying the whole city, and extending over anarea whose limits are not known. Several deposits of morelimited extent, and apparently of fresh-water origin, havebeen found in our own islands; as for instance at DolgeUy inNorth Wales, at Lough Mourne in Ireland (Fig. 102j, andin the island of MuU in Scotland. Similar deposits in Swedenand Norway are known under the name of berg-meld ormountain-flour; and in times of scarcity, the inhabitants ofthose countries are accustomed to mix these substances withtheir dough in making bread. This has been supposed merelyto have the eftect of giving increased bulk to their loaves, soas to render the reaUy-nutritive portion more satisfying. 336 MICROSCOPIC FORMS OF VEGETABLE LIFE. But as the berg-mehl has been found to lose from a quarter toa third of its weight by exposui-e to a red-heat, there seems a Fig. Fossil DiatomaeeoB, &c. from Mourne momitain, Ireland:—a, a, a,Gaillonella (Meloseira) procera, and G. granulata; d, d, d, G. bise-riata (side view); h, b, Surirella plicata; c, S. craticula; k, S. cale-donica; e, Gomphonema gracUe; f, Cocconema fusidium; g, Tabel-laria vulgaris; h, Piimularia dactylus; i, P. nobilis; I, Synedra ulna. strong probability that it contains organic matter, whichrenders it nutritious in itself.—When thus occurring in strataof a fossil or sub-fossil character, the Diatomaceous depositsare generally distinguishable as white or cream-colouredpowders of extreme fineness. 192. For collecting hesh Diatomace{S,thcee general methodsare to be had-recourse-to, which have been already described(§§ 143, 171). Their living masses, says Prof. W. Smith, present themselves as coloured fringes attached to largerplants, or forming a covering to stones or rocks in cushion- MODE OF COLLECTIX& DIATO:MACEiE. 337 like tufts—or spread
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