This is sometimes obviated by holing in the beds below the coal, or in any portion of a seam of inferior quality that may not be worth working.
The use of this machine has allowed a thin seam of cannel, from 10 to 14 in.
I bore is commenced at the dip, and reaches a seam of coal A, at 40 fathoms; at this depth it is considered proper to remove nearer to the outcrop so that lower strata may be bored into at a less depth, and a second bore is commenced.
In the South Wales system of working, cross headings are driven from the main roads obliquely across the rise to get a sufficiently easy gradient for horse roads, and from these the stalls are opened out with a narrow entrance, in order to leave support on either side of the road, but afterwards widening to as great a breadth as the seam will allow, leaving pillars of a minimum thickness.
Number and nature of the coal seams in new ground, or the position of the particular seam or seams which it is proposed to work in extensions of known coalfields.
Rich strips of alluvial soil, however, seam a cold clay-marl, needing intensive cultivation to become highly productive.
In driving levels it is necessary to cut grooves vertically parallel to the walls, a process known as shearing; but the most important operation is that known as holing or kirving, which consists in cutting a notch or groove in the floor of the seam to a depth of about 3 ft., measured back from the face, so as to leave the overhanging part unsupported, which then either falls of its own accord within a few hours, or is brought down either by driving wedges along the top, or by blasting.
It resembled that perpendicular seam sometimes made in the straight, lofty trunk of a great tree, when the upper lightning tearingly darts down it, and without wrenching a single twig, peels and grooves out the bark from top to bottom, ere running off into the soil, leaving the tree still greenly alive, but branded.
His tiny fist clutched the outer seam of her jeans.
The deep, short gorges and glens which seam the southern slopes of the Caucasus are inhabited by Ossetes, Tushes, Pshays and Khevsurs in the west, and by various tribes of Lesghians in the east.