﻿Vol. 64.] BALA AND LLANDOVEEY EOCKS OF GLYN CEIEIOG. 583 



that the component beds of the Dolhir Limestone sometimes bend 

 upwards as they approach the line of the fault. This would seem 

 to indicate that the direction of movement of the rocks above the 

 fault was downwards ; but we cannot consider this evidence con- 

 clusive, especially in view of the fact that the upward bend is 

 rarely seen. 



Besides this great strike-fault, there appear to be a number of 

 others of similar character which are, however, of considerably less 

 importance and cannot be traced for any great distance. The evi- 

 dence is most conspicuous in the neighbourhood of the second 

 ash-band, where the folding of the hard ash along with the softer 

 slates appears to have been accompanied by a considerable amount 

 of shearing and fracturing, and the boundary of the ash is fre- 

 quently a faulted one. This is particularly well shown at Cae 

 Deicws and Craig-y-Pandy. 



Near the China-clay Quarry the ash forms a line of crags which 

 runs up the side of the valley towards Cae Deicws. But, near the 

 top of the bank, a tongue of ash may be seen, separated from the 

 main line of crags by slates and sandstones, and apparently at a 

 lower stratigraphical horizon. This tongue, which does not extend 

 very far, we take to be a portion of the ash repeated by a fault of 

 rather low dip. In the quarry at Cae Deicws the effect of the 

 disturbance is clearly seen, and one of the subsidiary faults appears 

 to cause the curving of the columns shown on the right of hg. 8 

 (p. 563). On the opposite side of the valley, in the small quarry 

 at Craig-y-Pandy, there is a very distinct line of crushing and 

 slipping, presumably due to the same disturbance ; and the fact 

 that the beds immediately north of the ash do not strike parallel 

 to the band indicates a faulted boundary. 



At the southern margin of the China-clay Quarry there is a 

 small fault; and on the north-eastern side of this the ash is greatly 

 thickened, as if it had been crushed against the plane of movement. 



Further signs of crushing, along the northern boundary of the 

 same ash-band, are visible near Hafod-y-gareg, and the fault itself 

 may be seen in an old trial- working about 100 yards east of the 

 bridge. 



It is clear, therefore, that there has been a very considerable 

 amount of disturbance at the junction of the ash-band with the 

 slates above and below, and the boundary is often faulted. 

 Wherever this faulting is conspicuous, the ash is thickened and 

 appears to have been partly converted into the peculiar compact 

 rock resembling a quartz-porphyry, which has already been 

 described (p. 564). 



As will be shown in the account of the Cae-mawr Fault, there is 

 probably a thrust-plane at the foot of the isolated crag of ash east 

 of Llechrhydau. 



Several faults, probably of small importance, are visible along 

 ' the Glyn- Valley llailway, where this cuts through the Bryn Beds 

 a short distance below the Dolhir Fault. They dip at from 55° to 

 60° northwards. 



