Vol. 56.] SILtTRIAX SEQUENCE OE KHATADER. 109 



hollow representing the base of the Gafallt Beds (Bb) be traced 

 round from the preceding section it will be seen to ha?e approached 

 gradually nearer to the conglomerate-group, and at the line of the 

 fence, where it is scarcel) T more than 50 yards from the base of the 

 Lower Conglomerate, the two conglomerates appear to run up at 

 an acute angle to the groove, and disappear at a short distance 

 from it. Indeed this hedge forms the eastern limit of the con- 

 glomerate-group, for no sign of it can be detected to the eastward. 

 A section taken between the fence and Dol-Ifor Farm shows only the 

 Gafallt Beds (Bb) overlying the Gwastaden Group (A), and 

 these poorly exhibited in a prominent rib immediately south of the 

 farm (fig. 14, p. 106). The rock laid bare is a few feet only of hard 

 blue slate, with white grit-bands, none of which exceed ^ inch in 

 thickness ; in addition there are occasional seams of telepathic 

 sandstone. The whole group is weathered to the peculiar red 

 or orange colour of the M on o g r a ptu s - S e d g w i r/k ii Grits (BbJ. 

 Graptolites may be found in certain bands, but they are, as a rule, 

 badly preserved. I have, however, identified Monograptus Sedg- 

 ivickii, M. sp., Diplograptus Bughesii, and Glimacograptus normalis. 

 The Hhayader Pale Shales (0) are shown on the northern 

 bank of the western brook, and in the quarry north of Fron-dorddu, 

 where they dip south-eastward. 



(c) Additional Notes on the Caban Syncline. 



The preceding sections have been taken approximately in the 

 direction of the dip. The typical section running nearly north- and - 

 south, and the last roughly from east to west, would seem to indicate, 

 in the change of dip, some folding in the Caban Group, when 

 followed from west to east. If a section be produced from Caban 

 Coch to Allt-y-bont it will cross at right angles nearly all the 

 previous traverses, and show the structure of the Caban Group 

 between its eastern and western limits (fig. 15, p. 110). 



The typical section, though indicating the arrangement of the 

 Caban Beds on both sides of the gorge, does not, at the gorge itself, 

 follow the true dip, but runs more or less along the line of the strike. 

 In the river-valley at Caban Coch and for nearly | mile down the 

 Elau, the true dip of the rock is north-westerly, and at an angle 

 which may be anything from 10° to 40°. 



Commencing our section east of the Abernant Fault, we come 

 almost at once upon the Lower Conglomerate (Ba x ). In the 

 river-bed itself it was well exposed, as already mentioned, in the 

 Caban dam-foundations dipping north-eastward. This may be 

 followed round the west side of Cnwch Hill, where it sweeps up in 

 magnificent folds in the Craig Cnwch cliffs. 



The overlying shales (Ba 2 ), which are not shown in the river-bed, 

 are abruptly truncated by a cross-fault which brings down the 

 Gafallt Shales (Bb 2 ) against them. This fault is intersected 

 by two others, which bound the triangular mass of the Cnwch 

 Wood spur, and thus the whole of the block may be regarded as a 

 wedge dropped among its underlying beds by three boundary-fa ults. 



