﻿588 DR. T. GEOOM AND ME. P. LAKE ON THE [Ts"oV. I908, 



Of the easfcernmost of these two faults there appears to be further 

 evidence in the valley of Craignant, where the dips of the beds on 

 the two sides of the fault are very diflPerent, and where, moreover, 

 we have traced the narrow ash-band shown up to the western side 

 of the fault but not beyond. 



The West-North- West and East-South-East. Series 

 of Faults. 



The long fault belonging to this series in the western portion 

 of our map is most clearly seen far away to the west in the neigh- 

 bourhood of Corwen ; but its effects are visible, at intervals, along 

 its whole course. In our map (PI. LIII) it cuts off the prominent 

 hill of ash near Ty-isaf. Its continuation south-east of Hafod-y- 

 gareg is concealed, and in the map we have represented it as 

 ending against one of the other series of faults in the valley of the 

 Ceiriog ; but it probably continues beyond this. 



Another fault belonging to this series extends from Nant lorwerth 

 to Ty-nant. At the former locality it terminates the strongly- 

 marked grit-band near Bryn; at the latter it repeats the Craig- 

 y-Pandy Ash and the Coed-y-glyn intrusive sill. Its downthrow is 

 therefore to the south. An interesting point, in connexion with 

 this fault, is that it seems to end against the Dolhir strike-fault 

 already described. 



The remaining faults of this series are, to some extent, hypo- 

 thetical. That there is a fault along the valley of the Ceiriog 

 between Glyn and Dol-y-wern is clear, for otherwise the Ty-draw 

 Slates would extend across the stream and appear upon the northern 

 bank, where we actually iSnd Wenlock Beds. Whether, however, 

 this fault extends eastwards of the Cae-mawr Fault is at present 

 uncertain, but the valley of Ciluant lies in the same line. 



The fault drawn through the valley of Nant in the eastern part 

 of the map is necessary to explain the relations of the Carboniferous 

 Limestone on the north and the grey slates of Pwll-hir and the 

 grit of Gwernydd-gymmal on the south. Moreover, in the lower 

 part of the valley the whole of the northern bank appears to be 

 made up of "Wenlock Beds, and the whole of the southern bank of 

 pale slates. Exposures, indeed, are rare, so that certainty is not 

 attainable ; but the soil of the northern bank is full of fragments 

 of Wenlock Slate, the soil of the southern bank is equally full of 

 fragments of the pale slates, and there is very little intermixture. 



The dislocation of the Cwm-Clwyd Ash near Spring Hill, and of 

 the Glyn Grit near Gwernydd-gymmal, seems to be due to a long 

 fault which runs from W. 9° S. to E. 9° IS"., and appears to affect 

 the Carboniferous rocks also. The exposures between these two 

 localities are, however, so poor that it is scarcely possible to prove 

 that the dislocations are due to a single fault. 



