March 19, 1915. THE COLLIERY GUARDIAN! 613 THE GEOLOGY OF THE SOUTH WALES COALFIELD. THE PEMBROKESHIRE AREA. (Continued from page 332). Central Part of the Coalfield. (1) The Martletwy and Landshipping District.—This district may most conveniently be considered in two parts lying on opposite sides of a fault which traverses it from east-north-east to west-south-west; and which, passing close to the Landshipping Old Mill, a mile west of Martletwy, may be called the Old Mill Fault. The district north of this fault is comparatively undisturbed, and the higher coals especially have been worked for generations, though now information1 about them is difficult to obtain; the district south of it is highly disturbed, and the coals which occur, there have never been satisfactorily correlated with those to the north.' All attempts to prove definitely the existence of the important Timber Vein in that southern tract have been unsuccessful, though it is generally agreed that it must be represented among the veins which occur there. , . North of the Old Mill Fault.—The veins which, have been worked in this tract are as follows, in descending order • Bock Vein. Slate Vein (sometimes known as the .Tumbling Vein). Low Vein (of. the /Timber Vein Group). Big, High,/or Timber Vein. Little Vein. Stinkard Vein. Thin lower veins. .. The distances between these veins are liable to con- siderable change, and different accounts often vary within wide limits. On an average they may be assumed to be the same as in the Hook and Freystrop district. Among the lower veins the Stinkard Vein alone seems to have been worked to any extent; it obtained its name from the amount of “ sulphur ” it contains, probably in the form of iron pyrites. Its outcrop is marked, by abundance of ferruginous water which seems to be more characteristic of this than of any other of the lower veins. It is probably this vein which has been worked between Rigan Pill and Landshipping Ferry. The Little Vein has never been systematically worked. The principal vein, which corresponds to the Timber Vein of Jefireston and Bonville’s Court, is more usually known in this district as the Big Vein, or the High Vein, and has been worked extensively. Most of what is known of the underground structure of the area is derived from the workings of this vein. Its outcrop is usually made evident by the long deep trenches (“ reens ” of East Pembrokeshire) which have been dug in extracting the coal from among the mass of soft strata with which it is associated. This association and the great thickness of the vein also accounts for the exten- sive collapse of .the ground which has occurred where the vein has been removed. The Timber Vein, area north of the-Old Mill Fault is divided into belts, the boun- daries of which range in a direction a few degrees south of west, parallel to the Old Mill Fault and other dis- turbances which affect the region. The northernmost belt is limited on the north by the outcrop of the vein which runs a short distance south of Landshipping Ferry, and the “ Sandridge.String,” ranging from Black Wells Cottage to the north side of the small Land- shipping bay. Along it the Timber Vein outcrops with a vertical dip. In the Landshipping Colliery, a quarter of a mile north of the bridge, the Timber Vein was worked at a depth of 40 yds. The southern belt of Timber Vein workings lies under the Landshipping Valley and the small bay west of Landshipping Bridge. In this belt the Timber Vein forms a shallow syncline with comparatively little dis- turbance. Under, the valley it lay. at a depth of about 60 yds., but in the Merthyr Pit, close, to Millars Park, 300 yds. south-east of Landshipping Bridge, it was reached at 80 yds. The most recent workings in the vein were from the Garden Pit, 60 yds. south of the approach to the quay, where it lay at a depth of 65 yds. on the crest of a low anticline. In the Orielton Pit, 60 yds. to the south, the depth to the vein was 72 yds. The working of coal in this district was paralysed by. a disaster at the Garden Pit on February 2, 1844. The men were working somewhere under the middle of the river (the exact position is not known) when river water broke in; all were drowned,-and the whole of the work- ings were flooded. When the Westmeadow Colliery in the northern belt was restarted some years later the fear of encountering old flooded workings to the south prevented work in that direction. Of the Slate Vein very little is known. The Rock Vein, so called from having a massive quartzitic sandstone above it, occupies as a shallow syncline a small area on both sides of the western end of the Landshipping Valley. South of the Old Mill Fault.—The identification of the veins on the south of the Old Mill Fault presents con- siderable difficulties, because little work has been done on them, and that only along and near the outcrops. It deems generally agreed that the Timber Vein series must occur there, though that vein itself haAnot been recog- nised with certainty. An important attempt to prove this area was made when the Lady Berwick Pit (known also as the Old Mill Pit) was put down on the south side of the Landshipping Valley, near the Old Mill. Unfortunately the site chosen was close to, if not actually upon, the Old Mill Fault; it is also fairly certain that the measures at the surface there are considerably below the veins which are sup- posed to belong to the Timber Vein group on the south side of the fault. Several veins were passed through in the shaft, but most of them were thin and valueless. Another attempt to prove the veins in this area was made in the Westfield Slant, 170 yds. north-east of the farm, by Mr. John Roberts. It seems that much more systematic work is required on the south side of the Old Mill Fault before the existence of the Timber Vein group can be affirmed or denied. Southern Limit of the Martletwy-Landshipping Dis- trict.—To the south of the area where the7veins supposed to represent the Timber Vein group outcrop, there is a belt of ground in which two or three veins which are probably thin and of little value, have been worked only at and near the crop. Stratigraphically, these measures occupy a position above the Timber Vein Group, but when followed east- ward along the strike they range for the tract , of. ground south of Martletwy,' in which the rocks probably belong to the lower part of the coal measures, and one of the veins in this tract, which was worked north of Bush Farm, is stated to be the Lower Level Vein. . On the south they iare bounded by a folded belt of greenish-blue mudstones, with some shales and thin bands of laminated quartzitic sandstone, which are exposed along the foreshore south-west of Woodhouse, and are continued eastward towards Burnett’s Hill and Dugges Park. The junction between these two sets of measures is undoubtedly an overthrust from the south, but its magnitude is unknown. (2) Between the Eastern and the Western Cleddau.— In the belt of coal measures included between the Fare- well Rock and the Eastern and Western Cleddau only a few thin coals occur. Two veins appear to have been worked about three-quarters of a mile south of Picton Castle. A shale band exposed in the river bank 600 yds. north-west of Picton Point yielded the following marine fossils :—Ambocoelia cf. urei (Flem.), Chonetes lagues- siana de Kon., Chonetes sp., and Aviculopecten sp. nov. ? There was, therefore, at least one marine phase in the lower coal measures of this area. (3) The Coal District of Hook and Freystrop.—This Fig. 17;—Section oe Engine Bully at West Park Pit, Hook Colliery. S a N. Veins above TV Probably veins Supposec P'robablj Johnston once American below Bonney Low Igneous worked. Pit. T V Vein. Veins. Kocks. x Jr + A + Fig. 18.—Section across Freystrop Colliery. LEVEl SEA 5OO \ A Mile \ Scale toooFeet * ■ ~~ 2 Ft V 2 Ft V \ T.V. area, like that of Landshipping, is divided into narrow belts by faults ranging in an easterly direction .some of which have been proved in the workings to be over- thrusts from the south. These are most conspicuous in the Hook district, and their effects are especially shown by the displacements which the Timber Vein,, the prin- cipal seam of that region, has suffered. Between Little Milford 'and Freystrop Cross lower veins have been worked; the lowest vein is supposed to be the Kilgetty Vein. It lies some distance above a massive yellow 'weathering sandstone which is quarried near Middle Hill. The next higher vein is called the Plot Vein, and was said to be at a depth of 14 yds. in the Kilgetty Vein shaft. A higher vein, called the Ten-inch Vein, has been worked along the crop on each side of the main road about 300 yds. north of Freystrop Cross and appears to have been got also from some of the numerous shafts which occur along the south side of Little Milford Wood. ' Of the' lower group of veins the highest is the Two-foot Vein, which has been considerably worked for about a mile to the east of Freystrop Cross, and as far as Mount Pleasant, about a mile west of that place The three veins — the Plot, the Ten-inch, and the Two-foot .Veins ■— are probably responsible for the numerous crop workings near the south side of Little Milford Wood. These crops cannot be traced continu- ously, but appear to form a number of disconnected patches; it is probable that this is caused-by small over- thrusts. The principal vein of this district is the Timber Vein, but higher veins have been got in places. The veins of the upper group are as follows, the thickness of measures between them being only approximate as, owing probably to overthrusting, they are liable . to considerable variation :— Yds. Rock vein....................... — Measures ......................... 20 Tumbling vein ...................... — Measures .......................... 20 * Low vein ......................... — Measures .......................... 30 Timber vein....................... — Measures ................... 0 to 6 Bonney vein or Little vein . (Of no importance.) The main crop of the Timber Vein ranges, along the steep slope which overlooks the Western Cleddau from Underwood westwards, and thence along the ridge through Freystrop Cross to beyond Little Cranham. It is overlain by a considerable. thickness, of. tough quartzitic sandstone called the Timber Vein Rock, and underlain by a great mass of soft shales among which the Bonney Vein lies. The effect of minor overthrusting on these soft strata is probably responsible for the great variation in thickness of the vein, and for its frequent disappearance, along the line of outcrop., .This is ren- dered conspicuous by the long trenches of enormous width and depth ending abruptly at both ends; between them are gaps of 100 to 300 yds., where there is no trace of working, .and where the vein is said to have been pinched out altogether. Besides the surface workings, numerous shafts were put down on the vein. The Common Pit workings are bounded to the south by a large downthrow to the north, for on the north side .is the engine level course at 180 yds. below the surface, while on the south side are measures about the horizon of the Timber Vein, which crops at the mouth of the Pill Pit drift. In the belt of ground south of this fault the Timber Vein crops at the mouth of the Pill Pit drift, and again some distance to the east. In these workings the vein has a dip to the south.-east of about 25 degs. About 100 yds. south of Middle Hook the vein must crop again, for the Timber Vein rock is seen in the stream south of the farm dipping southwards at 80 .degs. Probably, therefore, another strike fault must pass near Middle Hook, ranging approximately parallel with the large fault to the north. . The Timber Vein was worked . also in the Sprinkle Colliery at a depth of 76 yds.; the strong dip in the Timber Vein rock, about 200 yds. to the west, would carry the vein to a greater depth than this, -so that the presence of another downthrow to the north is indicated. This is probably the same disturbance that was proved in the West Park workings, three-quarters of a mile to the west; the drift to the south (Engine Bully) met a disturbance of the nature of a sharp fold with vertical north limb, probably accompanied by an overthrust (fig. 17). Immediately to the . east of the drift the Timber Vein • workings on the south entered the. Low Vein on the north, the throw being therefore about 30 yds. The same disturbance was proved also in Nash Wood, one-third of a mile to the west. It ranges in a direction a little north of west, and might easily pass close to the Sprinkle Colliery. The Timber Vein along the south side of this disturbance is everywhere in a -vertical position. At the south end of the Engine Bully the vein was -abruptly turned up and pinched out against a . fault which again is probably an overthrust from the south, but its amount is not known. The Engine Bully disturbance seems to be indicated farther west near Strawberry Hill, where the Timber Vein lies at a considerable depth on its north side, but nearly crops as a string (i.e., in a vertical position) on the south.. . In the Freystrop Colliery east of Freystrop Cross thb Timber Vein appears to have been comparatively undisturbed. / An overthrust from the south must pass between the American. Pit and some veins north of Targate which are. said to be far' below the Timber Vein. This struc- ture. is in accordance with the prevalent structures all along the south margin of the Pembrokeshire coalfield, and would account for the fact that the Timber Vein was not met with in a long drift to. the .south from the pit, and also for the abrupt termination of the Timber Vein ground; along the same strike to the west only comparatively' barren measures occur, which- are probably low down in the coal measures. The belt of productive measures is bounded on the south by a narrow strip of measures in which at most only a few thin coals have been worked. In the absence of evidence to the contrary, it may be suggested from analogy with parts of East Pembrokeshire that they belong to a part of the coal measures lying below the Timber Vein group; especially as they are in turn followed southward either by millstone grit or by far older rocks. : Trials for Coal in Pre-Carboniferous Rocks.—There still lingers in Pembrokeshire and Carmarthenshire the idea that coal is to be found in certain rocks of the