BALA SERIES. 75 



a lower series of slates, mudstones, grits, and beds of arkose, with 

 a prevailing greenish-grey tint throughout, and devoid of fossils. 

 Notwithstanding their superficial resemblance to the Borrowdale 

 Series, these lower beds of the Ingleton area are not directly of 

 volcanic formation; and the term "Green Slates" was first 

 applied to beds developed to the west of Ingleton. At Chapel-le- 

 dale they are about io,opo feet in thickness, and they are 

 regarded by Prof. Hughes as of marine origin. In many respects 

 these beds belong more closely to the Welsh type of Bala rocks 

 than to that of the Borrowdale Series. (See p. 79.) 



Hirnant Limestone. 



This limestone is locally developed in the valley of Hirnant, 

 south-east of Bala, and in a tortuous tract between Bala and Dinas- 

 ]\Iowddwy. It was noted by Sedgwick in 1832. It is described 

 as a black impure pisolitic and fossiliferous limestone, containing a 

 few species of Orthis {O. Hiniantensis, O. sagitiifera, etc.), Area and 

 Modiolopsis, and stems of Encrinites. It occurs locally near the 

 junction of the Bala and the Llandovery Beds, and was considered 

 of Upper Bala age by Sedgwick. 



In Hirnant beds at Bwlch Hannerob, north of Aberhirnant, 

 Mr. Thomas Ruddy obtained Orlhis Himantensis, O. sagiiti/era, O. 

 eleganlula, O. bijorata, Lmgula ovata, Favosiii's fibrosus, Homalonotus 

 bisulcatiis, etc. The beds here consist of grits and shales, and 

 are from 50 to 300 feet in thickness. In other places there occur 

 concretionary lumps of limestone associated with the grits. Mr. 

 Ruddy believes that the Hirnant grits and limestone are identical 

 with beds that have been grouped as Lower Llandovery Grits. ^ 



It may also be mentioned that in Pembrokeshire and Cardigan- 

 shire, where the Llandovery group attains a great thickness, it 

 appears to rest conformably on the Bala Beds. Direct proofs of 

 unconformity are wanting in the neighbourhood of Corwen in 

 IMerionethshire, and in Denbighshire.- These instances of con- 

 formity may be due to accidental concordance in bedding, because, 

 as a rule, the Silurian beds rest irregularly on the Ordovician or 

 Upper Cambrian rocks. 



CORNWALL. 



Gorran Haven Beds. — The grey quartzites of Veryan Bay, and 

 other places south of Mevagissey, between St. Austell and Falmouth, 

 have been considered by Sedgwick (1851) and M'Coy to be of 

 Upper Bala age ; the fossils from Carn Goran (Gorran Haven) 

 being Orlhis calUgramma, O. scolica, Calymene hrevicapitaia, 

 C. parvifrons, Homalonotus bisulcatiis, etc. They were first made 

 known by the collections of Mr. C. W. Peach.^ Mr. Salter 



' Q. J. XXXV. 201. 



* H. Hicks, P. Geol. Assoc, vii. 295. 



' Q. J. viii. 13. I2th Report Cornwall Polyt. Soc. p. 66. 



