February 12, 1915. THE COLLIERY GUARDIAN. 331 furnace (see figs. 6 and 7). The top bar holders are bent to meet their angle iron supports fitted to each side of the boiler flue. These form a couple of flat tracks along which the coal is propelled direct from the hopper by means of two specially constructed screws running the whole length, so arranged that, while they are kept covered by the fuel as a protection against excessive heat, it (the fuel) is allowed to fall in desired quantities down the sloping sides to a midway position, where combustion takes place. A third screw at the bottom of the furnace pushes the fire along, deals with the ashes, and also serves as a clinker breaker. A fan forces air through the grating, while an auxiliary fan sends another draught of air to the bridge aperture, there to mingle with the flue gases and consume the black smoke. Dust is settled by a water supply in the ash trough. The underfeed stoker may be said to represent a com- plete departure from the principle underlying any of the contrivances that have up till now claimed our attention. The sectional sketch (fig. 8) will give some idea of the necessary alterations in design of furnace. In this particular instance, the coal is forced, by means of a worm, from the hopper through a sort of open duct fixed Fig. 6. ^SSSSSSSSSSSSSI Fig. 7. Fig. 8. below the grate. The revolutions of this worm are so regulated as to maintain a full charge, while at the same time pushing up just sufficient new fuel to keep pace with its continual consumption, besides giving longitudinal movement to the fire, without coming in direct contact therewith. Because of the absence of any undercurrent, com- bustion takes place only on the surface, leaving the congested mass below almost unaffected by the super- posed heat. The air, therefore, impinges upon the flames and mingles with the gases after passing through the over grids, laid lengthwise and sloping downwards to supporting brackets on each side the flue. Surface combustion, combined with underfeeding, is generally acknowledged to produce a good economical fire, so long as the machinery does its duty. But, according to the statement of several people who have had unfortunate experiences.of this class of stoker, the worms employed to work up the fuel gave a considerable amount of trouble, and were constantly being repaired, owing to frequent jamming of the coal. There is, however, another variety of underfeed stoker, which substitutes a metal floor for the usual grate. ! On this floor a layer of coal is deposited, the thickness of which is decided by the height of the angular end, over which the exhausted remains of the fire are passed. The air feed for combustion purposes is admitted over the top of the accumulation, while underneath several wedge-shaped scrapers are engaged in pushing forward fresh supplies, which in turn gradually lift the earlier deposits up to the level of the fire as consumption pro- gresses, and, at the same time, agitate the otherwise compact mass. These advancing and returning move- ments are actuated by a piston inside a steam cylinder. Boiler pressure is said to control the activities of this little engine so effectively that both fuel and air are admitted only in such doses as will correct any varia- tions and insure a level head of steam. Elevators for conveying the coal from bunk to hopper have proved a most useful and economical adjunct to the stoker itself. The sectional drawing (fig. 9) will serve to illustrate the absence of complication in the tackle employed. The lower end of the elevator, it will be seen, is provided with a strong iron “ shore ” or scuttle, which is con- stantly supplied from the heap tipped into the bunker, as a superposed agitator prevents the mass from clogging. A convenient slide at the inlet gauges the quantity of coal to be carried in each detachable bucket, suspended on an endless chain to the elevator head, where it is tipped and shunted down a couple of angular funnels into, the respective hoppers. The sprockets are put in and out of gear by a clutch coupled to the rope- driven pulley. A slide takes up any slack and main- tains the chain at an even working tension. Coal Conveying Plants. — The drawings, showing a fully equipped coal conveying plant, will serve to con- firm the contention in favour of a separate coal supply for each boiler, rather than depending upon one source for the whole range. The end elevation (fig. 10) gives a good impression of the general arrangement. A large hopper—capable in Fig. 9. Fig. 10. this case of holding 25 tons — is substituted for the detached bunkers. Here the coal is tipped and crushed before it is lifted, by means of buckets similar to those shown in fig. 9, to the right of the conveyor trough over the boilers. The conveyor itself consists of an endless wrought iron chain, having wide rectangular links to which a series of scrapers are attached. These push the fuel forward along the trough, whence it falls in desired quantities, through the bifurcated funnels, and into the stoking hoppers. Slides decide the amount to be delivered through each shoot, the respective apertures being gradually widened from the point of supply to the far end, in conformity with the gradually decreasing bulk. An overflow is provided to receive any temporary excess, which the attendant will rectify by means of a damper placed at the bottom of the general hopper. The trailing span of the chain, it will be noticed, is sustained by a number of rollers in order to prevent contact with the lower or working side. Scrupers are considered to be more economical than screw propellers, because they are less liable to suffer from overstrain, and are more readily renewed. Monetary Saving.—Apart from the saving in labour— more noticeable when elevators convey the coal from bunkers to hopper—’better general control, and more effective smoke abatement, we may naturally anticipate some monetary compensation for our additional outlay. In this we are not disappointed. A leading authority in the steam raising world estimates that so much as 33 per cent, better results are obtained over ordinary hand stoking by the use of mechanical stokers. Others claim efficiencies varying from 75 to 80 per cent, on so-called improved varieties. These figures must there- fore favourably reflect upon other economies, and subsequently find its way to the credit side of the coal account. THE GEOLOGY OF THE SOUTH WALES COALFIELD. THE PEMBROKESHIRE AREA. (Continued from page 280). Local Details. (1) The Coast Section, Amroth to Tenby. — Clear though this section is, the interpretation of the, structure, and the recognition of the larger overthrusts among the innumerable small slide planes that traverse the whole sedimentary mass, are far from easy. Certain seams, however, of anthracite and courses of “ mine ground ” (shale with bands and nodules of clay ironstone) have been extensively worked and identified at the various outcrops. These and the recognition of the millstone grit on either side of the coalfield have served as guides to the general effects of the disturbances. At the first glance an .impression is gained that a. southerly dip prevails throughout, but it will be found that the effects of the dip are counteracted, firstly by a succession of anticlines all presenting vertical or inverted faces to the north and slanting more gently down southwards, the effect being the same as that of an upthrow south, or of an overthrust from the south. Secondly, there are in addition to these several large overthrusts from the south, some of which follow the bedding approximately, and are not easy of detection. Lastly, close examination of the cliff shows that there has been great deformation of the whole sedimentary mass by movement along bedding places and along innumerable slide planes subsidiary to the main over- thrusts, and by the “streaking out” of some of the more plastic, as well as the crushing of some of the less yielding strata. Coal seams and carbonaceous shales were among the first to yield and to permit of movement between beds, the result being that what was once a seam with partings has been ground up into a schistose layer of variable thickness with no definitely recognisable coal in it. These black and greasy layers are known by the miners as “ dilsh,” and the finding of a coal seam in this condition is a serious risk in this coalfield. (2) The Northern Side of the Coalfield from Amroth to Yerbeston.—The coast section between Telpyn Point and Amroth reveals the lower part of the coal measures between the Farewell Rock and the lowest workable vein, the Kilgetty Vein. The thin impersistent vein which follows the Farewell Rock in the small bay west of Telpyn Point has been called the Tin Pits or Ten Pits Vein. A vein of fireclay and carbonaceous shale with some coal is known as the Lady’s Frolic Vein. The Lady’s Frolic Vein is succeeded abruptly by ferruginous current-bedded sandstones of a thickness of 40 to 50 ft.; on this rests the Kilgetty Vein, which is exposed in the road bank east of New Inn Cottage. The Kilgetty Vein is the lowest vein of any importance in the Amroth and Kilgetty districts. It has been exten- sively worked in association with the Lower Level Vein near Stepaside and Bonville’s Court. The following records have been obtained from the books of the Pembrokeshire Coal and Iron Company Kilgetty Colliery. Old Engine Pit, sunk in 1775 to the Kilgetty vein... 6 Croft Pit —— 99 ,, ... 76 West Park 1780 ’ ’ ,, ... 84 Quarry Park 1780 9 9 ,, ... 80 Deer Park 1781 99 ••• 80 White Gates 99 1787 99 ,, ... 84 Engine Pit 99 1789 9* ,# ... 56 Amroth Kill Pit 99 1798 ,, ... 84 Bedlam Pit 1805 ,, ... 20 William's Pit 1806 99 ,, ... 64 Thomas Hill Pit 1810 • • *• « 94 Pumping Pit • • 1840 99 ,» ••• 99 Wilson's Pit 99 1842 9‘ ,, ... 88 Thomas Chapel Colliery. Old Wheel Pit, sunk in Lays Pit 99 Stump Park Pit „ Hacket Pit „ Air Pit ,, Lower New Hays Pit „ Horse Wheel Pit ,, Pond Landing Pit „ Pond Engine Pit „ 38' 54 58 36 34 20 32 48 1784, to Lower Level vein 53 yards. 1784, ’ „ 1790, 1794, 1799, 1304, 1836, to Kilgetty Vein 1836, „ 1840, The hard rock pierced between 78 and 97 yds. iii the New Hays Pit is called the “ 27-fathom rock ” from the fact that it lies about that distance above the Kilgetty Vein, and also the “ 10-fathom rock,” in reference to its thickness. It outcrops a short distance to the south of the-Thomas Chapel Colliery, and . has been traced thence for some distance to the east and to the west. • To the north-west of Knaps this belt of measures is terminated by an important fault ranging in a north- easterly direction, and throwing down on the north-west. In the Martletwy district a vein-of coal or culm, over- lying a massive sandstone, has been largely worked in Boston’s Wood, nearly half-a-mile north of the village.