356

LLANDEILO FLAGS (CHARACTERS AND DISLOCATIONS).

are exposed in a thickness of nearly half a mile in highly inclined strata, (70° to 80°)on the hanks of the brook, extending eastward to the waterfall. Many casts of tri-lobites occur in these beds, and also bands of stone sufficiently calcareous to he burntfor lime.

The prevailing strike is here 30° south of west, whilst at Pentref and Tyr-wyn-fach, only onemile nearer to Llandeilo, beds charged with the same trilobites, are wrenched from the prevailingstrike and range, in vertical positions to the west, and even 10° north of west. If we trace thebeds to the westward across the valley of the Towy, we again meet with them greatly developed atLlandeilo, but in the very first ledge on the eastern side of the town they recover their south-westerly strike. This direction is however maintained a very short distance, for in the space occu-pied by even the high road, the same beds are broken off and trend on one side to the west, dipping80° to the north, or nearly at right angles to the beds observed upon the other. In most of thequarries in and about Llandeilo, the number of dislocations to which the flags have been subjectedis truly surprising, the strata being for the most part in vertical or highly inclined positions. (SeeMap, and PI. 34. figs. 7 & 8.) In one of the chief quarries of Dynevor Park, the beds are thrown socompletely out of the prevailing direction, as to strike E.S.E. and W.N.W., dipping 70° N.N.E.,whilst in Bird’s Hill they bend round from 15° W. of N. to true N.W., S.E., though in the Llan-gathen and Grongar Hills, the old strike of N.E., S.W. is resumed. In fact the beauty of DynevorPark depends upon these dislocations, by which the surface has been diversified and thrown intoseparate knolls now wooded to their summits. (See wood-cut at the head of this chapter, DynevorPark in the foreground, Golden Grove in the distance.)

The prevailing flagstone, in beds from two to four inches thick, is dark-grey orindigo colour when extracted, but it weathers to a light ashen hue, the surface beingin some parts covered with a profusion of casts of the Asaphus Buchii, other organicremains being rare. The calcareous flags are very generally traversed by veins of whitecalcareous spar, from one-tenth to half an inch wide, which usually divide the beds intorhomboids. These flags occasionally, as at Grug, about three quarters of a mile north-west of Llandeilo, pass down into thicker masses of sub-crystalline, dark, impure lime-stone, having an east and west strike, and a dip of 45° to the north. They containencrinites, a few casts of shells, Asaphus Buchii and A. tyrannus. The beds have acorrugated surface, due to the mass being composed of small irregular concretions, andthis structure is partly occasioned by the unequal dissemination of sand and even ofsmall pebbles in the calcareous matrix. The true flag-like structure of the Llandeiloflags is not discernible in any of these beds. The Grtig quarries exhibit the oldestcalcareous beds of this formation, as they lie to the west and north-west of the flags,and the same nodular limestones occur in Llangathen and Grongar Hills in similarpositions, rising from beneath the younger strata and graduating on their western flanksinto the rotten slates and grey wacke grits of the inferior or Cambrian System, in which(in this district) all traces of fossils are lost.

To the south-west and west of Llandeilo the flagstones are found on both banks of the Towy indistorted masses, none of which have a continuous strike for more than a few hundred paces. Below