﻿Vol. 64.] BA.LA. AND LLANDOVERY EOCKS OF GLYN CEIRIOG. 549 



far from the horizon of the Bala Limestone, and that the passage 

 upwards into the Denbigh Plags is apparent rather than real. 



Daniel Sharpe, in his ' Contributions to the Geology of North 

 Wales,' gives some details concerning this district, and his map 

 shows several intrusive masses in the neighbourhood of the Ceiriog. 

 In his notes he expresses his indebtedness to a manuscript map by 

 Bowman for this portion of North Wales. 



The Geological-Survey map of the district was published in 1850, 

 and again, with alterations and additions, in 1855. It seems to 

 have been largely the work of Jukes, and extracts from his notes 

 will be found in the chapter on the Berwyn Hills in Ramsay's 

 memoir on the Geology of North Wales. Three bands of ash are 

 traced upon the map, and two bands of limestone, the lower of 

 which is considered to be on the horizon of the Bala Limestone. 

 The Tarannons are represented as unconformable on the beds 

 below. The boundary drawn upon the map is nearly correct ; 

 the simulation of unconformity is, however, due to faulting, which 

 affects not only the Tarannon and Wenlock Beds, but also the 

 beds below. 



On the Geological-Survey map no Llandovery beds are recognized 

 in the district, and the Tarannon Shales are represented as resting 

 directly on the Bala Series. In a letter to the ' Geological Magazine ' 

 in 1867, Salter suggests that the upper limestone of Mynydd Pron 

 Frys may be the equivalent of the Hirnant Limestone, and that the 

 northern end of the hill probably consists of Llandovery rocks. He 

 also says that the hill of Pentre and the slopes above Tal-y-garth 

 are almost certainly Llandovery. In a subsequent letter, D. C. 

 Davies states that he had already arrived at the same conclusion. 



The fullest account of the local succession which has yet appeared 

 is to be found in a series of papers by D. C. Davies, and despite 

 certain errors in interpretation, which detract from the value of 

 his work, his account is so near to the apparent truth that it will 

 be well to give his results in some detail. 



Of his several papers we may take that of 1872 (published in 

 1873) as representing his final conclusions. In the second section 

 accompanying this paper (Proc. Geol. Assoc, vol. ii, p. 303) — a 

 section from Pont-y-Meibion to Pont Dolwern — he recognizes the 

 following subdivisions, in descending order : — 



f 



(13) Wenlock Shale. 



(12) Llandovery Beds (very fossiliferous). 

 (11) Hirnant Limestone. 

 Bala I (10) Fossiliferous shales. 

 Beds. | (9) Bala Limestone. 

 [ (8) Ashy beds. 

 ~f (7) Shales and slaty beds. 



(6) Massive felstone and ashy beds. 

 Llandeilo ' ^^^ Dark limestone. 



■D ■{ (4) Sandstones and shales. 



I (3) Porphyritic beds. 

 I (2) Dark pyi-itous shales, 

 \^ (1) Compact greenstone. 



