. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. V.] CREEPS IN COAL-MINES. 51 act amount of depression in these cases can only be accurately measured where water accumulates on the surface, or a railway traverses a coal-field. When a bed of coal is worked out, pillars. or rectangular masses of coal are left at intervals as props to support the roof and protect the colliers. Thus in fig. 66, representing a section at Wallsend, Newcastle,. 0-o the galleries which have been excavated are represented by the white s
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. Ch. V.] CREEPS IN COAL-MINES. 51 act amount of depression in these cases can only be accurately measured where water accumulates on the surface, or a railway traverses a coal-field. When a bed of coal is worked out, pillars. or rectangular masses of coal are left at intervals as props to support the roof and protect the colliers. Thus in fig. 66, representing a section at Wallsend, Newcastle,. 0-o the galleries which have been excavated are represented by the white spaces a b, while the adjoining dark portions are parts of the original coal-seam left as props, beds of sandy clay or shale constituting the floor of the mine. When the props have been reduced in size, thev are pressed. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Lyell, Charles, Sir, 1797-1875. New York, D. Appleton and co.
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Keywords: ., bookcentury1800, bookdecade1860, booksubjectgeology, bookyear1868
