72 PALEOZOIC TIME. [CHAP. VI. 



in a distance of twenty to twenty-five miles ; if its attenuation 

 continued at the same rate it must have died out some ten 

 miles north of the Forest of Dean coalfield, i.e. a little to 

 the south of the 52nd parallel of latitude, and as a mat- 

 ter of fact it appears to be absent at Newent. The same 

 northerly thinning occurs throughout the South Wales 

 coal-basin, the Limestone series on its southern border 

 being variously stated as from 1,000 to 2,000 feet thick, 

 while along the northern border it is not more than 500 

 or 600 feet thick, and near Haverfordwest it appears to 

 die out altogether, and to be overlapped by the Coal- 

 measures. These facts may be taken as indicating the 

 existence of land a few miles north of the present boundary 

 of the limestone. 1 



From Pembrokeshire we pass across to the coast of 

 Wexford in Ireland, and as we find very similar conditions 

 existing there, it is exceedingly probable that the coast-line 

 we are following was continuous from Pembroke to Wex- 

 ford. Carboniferous rocks occur round Wexford Harbour, 

 and extend south-westward in a narrow strip between 

 areas of Cambrian rocks, and are found again on either 

 side of the entrance to Waterford Harbour. Mr. Kinahan 

 states that the dark shales and limestones which are found 

 along the southern margin graduate into red shales, sand- 

 stones, and conglomerates along their northern margins, 

 and that " these rocks seem to have accumulated in a 

 narrow bay which shallowed out eastward." 2 



That the Cambrian, Ordovician, and Granitic areas of 

 Wexford, Carlo w, and Wicklow were land at the time 



1 That the thinning of the limestone was in the direction of land, and 

 not away from it, is shown by the simultaneous thinning of the Mill- 

 stone grit and the overlap of the Coal-measures. We know also that 

 the Carboniferous limestone was often formed in close proximity to 

 shore-lines. 



8 " Geology of Ireland," G. H. Kinahan, p. 78. 



