76 PALAEOZOIC TIME. [CHAP. VI. 



westward. It is, of course, possible that there was com- 

 munication by way of a narrow strait between the Cariing- 

 ford area and that of the Isle of Man, but the evidence on 

 the Irish side is in favour of there having been a con- 

 tinuous mass of land over the western part of the Irish 

 Sea, and the Manx rocks are just as likely to have been 

 formed in a bay on the eastern side of this land, seeing that 

 there were several such bays on the western side. 



Exactly the same reasoning applies to the Carboniferous 

 rocks of Anglesey. The succession here is very similar to 

 that of the Isle of Man a basal conglomerate, succeeded 

 by red sandstones and cornstones from 200 to 300 feet 

 thick, overlain by limestones only 450 feet thick, and 

 covered directly by the Millstone Grit. These small thick- 

 nesses suggest the neighbourhood of land, and that this 

 lay to the west is shown by the fact of the Limestone series 

 rapidly thickening to the east, and attaining some 2,000 

 feet in the north of Flint. It is quite possible, therefore, 

 that the western part of Anglesey was land, and that the 

 Carboniferous beds were deposited in a bay or inlet which 

 penetrated into this land, and narrowed south-westward. 



Patches of limestone skirt the coasts of North Wales 

 and border the Silurian rocks along the Vale of Clwyd ; 

 here and in North Flint its thickness is about 1,500 feet, 

 and it keeps this thickness for some distance southward, 

 being still 1,200 feet thick at the north-west end of the 

 Eglwyseg escarpment near Llangollen, where it rests on 

 300 feet of yellow sandstone and conglomerate. Thence, 

 however, it thins very rapidly to the south-east, being only 

 600 feet thick at Trevor, and under 200 feet at Fron-y- 

 Cysyllte on the south side of the Dee ; thus, in a distance 

 of four miles, the red sandstones and about 1,000 feet of 

 the limestone have thinned out against a slope of Silurian 

 rock, a fact which suggests the existence of an island in 

 the sea of the Lower Limestone near Euabon and Chirk. 



