92 Physical Geography. 



Ludlow are more than 3,000 feet in thickness. The 

 original extent of this long-buried island, may have 

 been about 24 miles in length by 14 in breadth, about 

 the size of the Isle of Man. 



The same fate was undergone by the Llandeilo and 

 Caradoc rocks, that with lavas, ashes, and intrusive 

 greenstones, now lie between Builth and Llandegley in 

 Kadnorshire. This island was, however, lower and 

 smaller, its length having been about 20 miles, by 10 

 at its greatest breadth. 



That these two tracts of land stood as islands in an 

 early Upper Silurian sea, I have no doubt ; and on 

 grounds less definite, I am of opinion, that at the very 

 beginning of the Upper Silurian epoch, the greater part 

 of Wales, both south and north, formed land, some of 

 it higher than now, for since that time the Lower 

 Silurian rocks of that region have undergone great and 

 repeated denudations. As, however, the deposition of 

 the Upper Silurian formations progressed, a steady 

 submersion took place of the neighbouring land, from 

 the waste of which, sediments were derived ; but 

 whether or not its highest mountains were swallowed up 

 and buried before the close of the Upper Silurian epoch 

 I am quite unable to say. That this entire burying of 

 the Lower Silurian rocks of Cumberland took place, 

 seems most probable ; and while the Lower Silurian 

 rocks of the Highlands of Scotland, and the West of 

 Ireland, certainly formed high land during the begin- 

 ning of Upper Silurian times, I have no precise data 

 by which to determine what was their subsequent fate. 



A section of the Silurian strata, as seen near Caer 

 Caradoc and Wenlock, is shown in fig. 22. 



The same kind of development passes southward 

 beyond Ludlow, forming beautiful scarped woody ter- 



