168 DISLOCATIONS ALONG THE MARGIN OF THE SOUTH WELSH BASIN.

the abrupt escarpment of the chief mass, that the carboniferous limestone must oncehave extended over a considerable portion of the valley, and probably far to the west-ward of the castle. It is also evident from the opposite inclination of the strata oneach side of the gap at Cwrt-a-barddh and from the beds on which the castle standsdipping away from the main escarpment, that the whole of the district has been vio-lently broken up. We have therefore data for inferring, that the part of the valleysituated between the outlier and the boundary of the coal-field was once the scene ofa great disturbance, and that a body of water similar to that we have supposed to bein existence in the case of Pen Cerrig Calch (p. 162.) has subsequently removed theintervening masses of strata, leaving the Cerrig Cennen a monument of its devastatingaction.

It is not my intention to describe the other dislocations in the carboniferous limestoneon the south-western edge of the South Welsh coal basin, as they will form a portionof Mr. Conybeare’s memoir. It is sufficient to say that they all exhibit, though some-times in a minor degree, nearly the same phenomena as have been here delineated.Some of the general inferences which may be deduced from these facts will be noticedin a subsequent chapter, after the reader has been made acquainted with the disruptionsof the older rocks.

Repeating, however, an observation deduced from similar phenomena in the CleeHills, I will here merely observe, that the method by which the strata surrounding andsupporting this coal-field have been fashioned into the broken margin of a basin, isclearly indicated by numerous and powerful transverse dislocations 1 .

1 See p. 119.