﻿Vol. 64.] BALA AND LLAT^DOVERY ROCKS OF GLT]!^ CEIRIOG. 547 



themselves, and thereby a considerable portion of the succession is 

 cut out. Such a fault is not easy to detect ; but we have now traced 

 it from east to west for a distance of 5 miles, and there is evidence 

 that it extends considerably farther westwards. 



Owing to the difficulty of detecting faults of this nature, it is 

 quite possible that there may be others that we have overlooked ; 

 but, if so, their effect appears to be unimportant, and (excepting for 

 the fault already noticed) the succession in the Grlyn Valley seems 

 to be unbroken. 



We have failed to discover any evidence of unconformity between 

 the supposed Corwen Grit and the Bala Beds below ; and the fossils 

 obtained from the grit (which is here often calcareous) agree very 

 closely with those from the uppermost Bala Beds of the district. 

 The most important palaeontological break occurs, not at the base, 

 but at the top of the grit, between the latter and the Llandovery 

 Slates above. The grit itself must, therefore, belong to the Bala 

 Series. Since, however, there are certain palaeontological differ- 

 ences between the beds immediately below the grit at Corwen and 

 those immediately below the grit at Glyn, it is possible that the 

 Glyn Grit may not be the precise equivalent of the Corwen Grit. 

 On this point we prefer, for the present, to suspend our judgment, 

 and to confine ourselves to the statement that the grit at- Glyn 

 belongs definitely to the Bala Series and not to the Llandovery. 



11. Literature. 



1841. J. E. Bowman. 'Notice of Upper Silurian Rock? in the Vale of Llan- 

 gollen, North Wales ; & of a Contiguous Eruption of Trap & Compact 

 Felspar' Trans. Manchester Geol. Soc. vol. i, pp. 194-211, & 2 sec- 

 tions (on pi. vi). 



1843. Adam Sedgwick. ' On the Older Palgeozoic (Protozoic) Eocks of North 

 Wales' Proc. Geol. Soc. vol. iv, pp. 251-68, with map & sections. 

 See also Quart. Journ. Geol. Soc. vol. i (1845) pp. 5-22. 



1846. Daniel Sharpe. 'Contributions to the Geology of North Wales' 

 Quart. Journ. Geol. Soc. vol. ii, pp. 283-316, & pis. xii (map)-xiii. 



1850, Geological Survey, Quarter-sheet 74 SE. Re-issued, with alterations, in 

 1855. 



1859. D. 0. Davies. 'The Geology of Glyn Ceiriog' Oswestry & Welsh- 

 pool Nat. Field-Club & Arch. Soc, Report of Meetings 1857-64 

 (1865) pp. 32-36. 



1864. D. C. Davies. ' On the Bala Limestone & its Associated Beds in North 



Wales ' Proc. Liverpool Geol. Soc, Session 5, pp. 21-30, with one 

 section. 



1865. D. C. Davies. ' List of Fossils described from the Bala Limestone & its 



Associated Beds of North Wales' Proc. Liverpool Geol. Soc, Session 6, 

 pp. 30-34. 



1865. D. C. Davies. 'A Walk over the" Ash-Bed" & " Bala Limestones " near 



Oswestry ' Geol. Mag. vol. ii, pp. 343-47, with one section. 



1866. A. C. Ramsay. ' The Geology of North Wales ' Mem. Geol. Surv. vol. iii. 



1867. J. W. Salter. * Bala & Hiruant Limestone ' (Letter) Geol. Mag. vol. ir, 



pp. 233^34. 

 1867. D. C. Davies. 'Bala & Hirnant Limestones at Mynydd Fron Frys in 



Glyn Ceiriog' (Letter) Geol. Mag. vol. iv, pp. 283-84. ' 

 1872. D. 0. Davies. ' On the Overlapping of several Geological Formations 



on the North Wales Border ' Proc Geol. Assoc, vol. ii (1873) 



pp. 299-308, with map & sections. 



