88 SILURIAN. 



LLANDOVERY BEDS. 



The name was given by Murchison, because the strata are well 

 developed near Llandovery, in Caermarthenshire. The beds con- 

 sist of sandstone, grit and conglomerate, slate and shale, attaining 

 a thickness estimated at 2500 feet, though frequently it is much less. 



Lower Llandovery Beds. 



These rocks consist of hard grey grits and conglomerates, with 

 beds of slate and shale, and attain a thickness of from 600 to 1000 

 or even 1500 feet. 



Among the fossils are Petraia iiniserialis, Halvsites catenidarius, 

 Calymene Blumenbachii, Orthis eleganttda, Strophomcna, Pciitameriis 

 {Stricklandmia) lens, Meristella crassa, etc. Casts of Pcntameriis 

 obhmgus are occasionally met with in the rocks. 



To the west of Builth and near Llandovery the beds appear to be 

 most fossiliferous. Fossils have also been recorded from Pen-y- 

 Craig in Caermarthenshire; from Llangyniew, Mathyrafal, and 

 INIeifod, in Montgomeryshire ; and from the Quaker's Burial Ground 

 in Pembrokeshire. 



The Lower Llandovery strata appear south-east of Bala Lake, and 

 are developed over a great part of South Wales, near Rhayader, 

 Garth, north-west of Builth, etc. The junction with the Upper 

 Llandovery beds is seen near Noeth Grug, north-east of Llandovery. 

 These rocks extend over a good deal of country on the borders of 

 Cardigan Bay, between Aberystwith and Cardigan, and are exposed 

 at Haverfordwest. To the south of Haverfordwest shelly sand- 

 stones are exhibited, which overlie conglomerates that form the 

 base of the Silurian system.^ 



Upper Llandovery Beds or May Hill Sandstone. 



These rocks consist of grey and yellowish sandstones, grits, and 

 conglomerate, attaining a thickness of about 800 feet. Sometimes 

 a calcareous band is met with : as, for instance, the Norbury Lime- 

 stone and Hollies Limestone, in Shropshire, From the abundance 

 of Pcntamerus, these strata are termed the Pentamerus-beds, or zone 

 of /*. oblongus. 



The May Hill Sandstone yields species of Corals, Favosifes, 

 Heliolites inteistincta, Petraia rugosa, P. elo7igata, and P. bina. Also 

 Annelides, Trilobites, and Mollusca, the Brachiopoda being most 

 abundant. Amongst the species are Pentameriis oblo7tgus, Atrypa 

 reiiculans, Orthis proiensa, Strophoiiiena compressa, S. aniiquata, 

 JMurchisojiia, Belleropho^i trilobatus, Encri7uinis punclatus, etc. 



1 J. E. Marr and T. Roberts, Q. J. xli. 489. 



