90 Llandovery Beds. 



strata wherever they occur, were often beaches of the 

 period ; and this is further proved by the fact that they 

 are often conglomeratic, containing rounded pebbles 

 derived from the rocks on which they rest, while, as at 

 May Hill and Woolhope, they are coarsely sandy. 



From these facts we arrive at the conclusion that 

 during the beginning of Upper Silurian times, part of 

 FIG. 20. 



1. Cambrian rocks. 



2. Pentamerus limestone and conglomerate. 



the area now called Wales consisted of islands formed 

 of Lower Silurian strata and volcanic rocks, round 

 which the occasional consolidated beaches are still 

 visible. 



Groing further into the physical geology of this epoch, 

 we find that in South Wales the Upper Llandovery 

 beds lie unconformably on a large scale on the Llandeilo 

 and Caradoc series, a fact proved by the conflicting 

 dips and strikes of the two sets of strata; while in 

 North Wales, similar conflicting strikes, and the steady 

 overlapping of the Upper on the Lower Silurian beds, 

 proves the same fact, for east of Bala the base of the 

 Upper Silurian beds lies about 2,000 feet above the Bala 

 Limestone, while in the neighbourhood of Conway they 

 almost touch that horizon. 



Another important point connected with the physi- 

 cal geography of the period is that, after a time, the 

 Lower Silurian islands and other areas began to undergo 

 a process of slow depression beneath the sea. If we 



