90 SILURIAN. 



In South Wales these beds first appear in Marloes Bay, and, at 

 intervals, range across Pembrokeshire ; but further north and east 

 they disappear for a space, being overlapped by the Old Red Sand- 

 stone. They re-appear south of Llandeilo and, varying from a few- 

 feet to 1000 feet in thickness, they range north-east in a narrow strip 

 through parts of Caermarthenshire, Brecknockshire, and Radnor- 

 shire, lying indifferently upon Lower Llandovery, Caradoc, or 

 Llandeilo Beds. Near Builth, where they are only a few feet thick, 

 they rest unconformably upon the Llandeilo Flags and their as- 

 sociated igneous rocks. They are also found near Presteign, where 

 they are locally called ' Gorton grit.' They occur at Nash Scar, 

 and in Shropshire they lie unconformably on the Caradoc Sand- 

 stone, between Cardington and Coalbrook Dale. In the Long- 

 mynd country they also lie quite unconformably (in the form of a 

 calcareous conglomerate) on Cambrian rocks, and beyond this in 

 Wales they are not known anywhere at the western base of the 

 [Silurian] strata between Radnorshire and the mouth of the 

 Conway.^ The Upper Llandovery Beds are well known at May 

 Hill and Huntley Hill in Gloucestershire. (See Fig. 12.) They con- 

 sist of sandstone and shale, with conglomerate. They occur also 

 at Gharfield Green and Stone, near Tortworth in Gloucestershire, 

 where fossils have been obtained ; and here they comprise red 

 micaceous sandstone and grit, with subordinate beds of shales, 

 and sometimes limestone. At Malvern they consist of grey and 

 purple laminated sandstones and shales, about 500 feet thick, 

 resting on grey and purple sandstones and conglomerates, about 

 600 feet thick. ^ (See Fig. 14.) Here and in the Abberley Hills 

 many fossils have been collected. 



In North Wales the Llandovery Beds are represented by the 

 Corweti Grits described by Prof. Hughes in 1876. These grits, 

 which take their name from Corwen, in Merionethshire, consist of 

 fine sandstones and grits, sometimes containing quartz pebbles. 

 They yield species of Favosites, Pdraia, Orthis, etc. The beds 

 may be seen near Corwen and Penyglog. In places they are 

 worked for road-metal. At Nant Llechlog there is a white saccha- 

 roid sandstone. The beds rest unconformably on the Bala Beds, 

 and are overlaid by " Pale Slates " (Tarannon Shales). Certain 

 mudstones at Llansantffraid appear locally to represent the Corwen 

 Grits. ^ The May Hill group may also be represented near Treior- 

 werth in Anglesey.-* Fossils have been collected from the neigh- 

 bourhood of Presteign, in Radnorshire ; Builth, in Brecknockshire; 

 Llandovery, Llangadoc, and Pen-y-lan, in Caermarthenshire ; and 

 Marloes Bay and Wooltack, in Pembrokeshire. 



In the Dee Valley, the Cerrig-y-druidion grits are grouped by 

 Mr. J. E. Marr with the Corwen Grits and May Hill Group.* They 



1 Ramsay, Geol. N. Wales, edit. 2, p. 18. 



2 Phillips, Mem. Geol. Surv. vol. ii. part I. 

 ^ Q. J. xxxiii. 207. 



* T. M'K. Hughes, Q. J. xxxvi. 239. 



* Q. J. xxxvi. 278. 



