. Bulletin of the Geological Society of America. Geology. 430 PROCEEDINGS OF MONTREAL MEETING. is in the " block" coal-field, where the coal-beds are thin, ranging from 3 to 5 feet in the centers of the basins to a few inches or nothing between basins. These beds are in this area sometimes found thickened up to 10 or 12 feet—that is, from three to four times their normal thickness. Figure 2 shows the detail, in part, of a thickened bed from Columbia No. 3 mine. In this case the coal-bed, normally 3 feet 4 inches thick, has been compressed until 12 feet thick. As might be. Figure 2.—S
. Bulletin of the Geological Society of America. Geology. 430 PROCEEDINGS OF MONTREAL MEETING. is in the " block" coal-field, where the coal-beds are thin, ranging from 3 to 5 feet in the centers of the basins to a few inches or nothing between basins. These beds are in this area sometimes found thickened up to 10 or 12 feet—that is, from three to four times their normal thickness. Figure 2 shows the detail, in part, of a thickened bed from Columbia No. 3 mine. In this case the coal-bed, normally 3 feet 4 inches thick, has been compressed until 12 feet thick. As might be. Figure 2.—Sketch of detailed Structure of Part of a 3-foot U-inch Coal Bed locally thickened to 12 feet. expected, the coal which is obtained at such points simply crumbles into slack when mined. At one point the strata in general have suffered until the two coal- beds worked in this area, which normally are 20 to 30 feet apart, are brought to within 6 inches of each other, the lower bed being at that point thickened up to 4? feet and the upper bed from 4 to 6% feet. In a third direction the evidence comes from the peculiar joint structure com- mon in this area. As stated above, this area lies in the ''block" coal-field, where joint structure is developed in the greatest perfection. Figure 3 shows the normal joint structure of block coal. Figure 4 shows the way the same structure appears over most of this area. In some parts of the mines of this disturbed district the. 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 Geological Society of America. [New York : The Society]
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1890
