BALA SERIES. 7I 



black calcareous shales and flags, followed by limestone, rest 

 conformably on the Llanvirn series. The upper beds comprise 

 black slates, flags, and flaggy sandstones. The black limestone of 

 Llan Mill, and Lampeter Velfrey, Haverfordwest, which is inter- 

 stratified with black shales, and contains Asaphus iyrayinus, etc., 

 is regarded as Llandeilo limestone.^ Mr. Salter thought that some 

 of the fossils from the Budleigh Salterton pebble-bed (New Red 

 Series) might belong to the Llandeilo rocks.'* (See sequel.) 



In South Wales there are slate-quarries in Aber-eiddy Bay ; and 

 in North Wales slates are worked at the Hendre Dhu or Prince 

 Llewellyn quarry, at Dolgarth or Pennant Vale quarry, Dinas Lake, 

 Snowdon slate quarry on Bwlch Cwmllan, near Beddgelert, between 

 Bettws-y-Coed and Capel Curig, at Dolwyddclan, and in the Corys 

 (or Corris) and Ffestiniog districts. 



BALA OR CARADOC BEDS. 



The Caradoc Sandstone was first noticed by Murchison in 1833, 

 and in 1834 he described the strata under the name of Horderiey 

 and May Hill Sandstone. Subsequently, in the Silurian System 

 (1839), they were termed Caradoc Sandstone from the circumstance 

 of their being typically developed in the neighbourhood of Caer 

 Caradoc, in Shropshire, a hill which rises to a height of 1200 feet. 

 In 1838 Sedgwick described the Bala rocks from the Bala district 

 in Merionethshire, and regarded them as forming the upper part of 

 his Cambrian system. Salter, in 1853, from an examination of the 

 fossils, concluded that the Bala Beds were generally identical with 

 the Caradoc Sandstone.^ 



The Caradoc and Bala beds consist of sandstones, flags, shales, 

 slates, and limestones, with interbedded volcanic rocks. They 

 constitute the Upper Caradoc group of John Phillips (1842); and 

 a portion of the Snowdonian group of Sedgwick. 



Dr. Hicks has divided the beds as follows •} — 



■Rila ( ^PP^''- — Shales, flags, and limestones. \ 



-r. 1 \ Loiver. — Sandstones, shales, grits, calcareous bands, \ ,J'^ r . 



-beds. J 1 • ' 1 jj J 1 I 12,000 feet. 



\ and interbedded ash. ; ' 



The beds vary in thickness considerably in different districts in 

 consequence of the uneven distribution of interbedded volcanic 

 rocks. They rest conformably on the Llandeilo rocks. They 

 are developed at Bala, Snowdon, Anglesey, Caradoc, Horderiey, 

 Norbury, Haverfordwest, Llandeilo, etc. 



The Bala Beds are particularly rich in Trilobites and Brachiopods, 

 but they include many other forms of life. Among these are 



^ J. E. Marr and T. Roberts, Q. J. xli. 477. 

 2 G. Mag. 1864, p. 6. 



' A. C. Ramsay, Geol. N. Wales, edit. 2, p. 6. See also Sedgwick, Q. J. 

 viii. 47 ; and D. Sharpe, Proc. G. S. iv. 10. 

 * Q. J. xxxi. 192. 



