part 4] district around corris and abekllefenni. 535 



the north side of Nant y Goedwig, the pitch is again 35°. In fact, 

 in most localities where it is possible to take direct observations of 

 tbe pitch, the values vary between 30° and 35° and rarely less. 

 However, it is unlikely that this value is maintained continuously 

 along the axis of the folds. It is probable that the crests of the 

 folds are of an undulatory character : that is, at one point the 

 pitch is considerable, then diminishes, and then steepens again. If 

 that be so, then the average pitch in the area is considerably less 

 than 30° or 35°. 



In this respect it is interesting to observe the form of the 

 outcrops of successive rock-groups in the Corris Anticline. The out- 

 crop of so well-deHned a band as the perse ulptus zone makes a broad 

 Y pointing southwards indicating a strong southerly pitch. The 

 equally conspicuous outcrop of the grit-band in the Garnedd-Aven 

 Beds be 1 ^-" .aakes a narrow V, such indeed, that for some distance 

 the outcrops in both limbs of the fold are approximately parallel 

 one to the other. This feature is again well shown in the form of 

 the outcrop of the Narrow Vein farther north, where the outcrops 

 on the two limbs of the anticline are practically parallel for a dis- 

 tance of over half a mile. The western outcrop of the Narrow Vein 

 in this locality is capable of accurate mapping, for it is continuously 

 exposed in a series of open-air workings. The eastern limb is not 

 quite so Avell exposed for part of its outcrop ; but there can be no 

 doubt of its location within a few feet, because exposures of the 

 characteristic beds above and below are numerous. It is possible, 

 however, that part of the Narrow Vein may be cut out by faulting 

 on this eastern limb, but I have found no evidence of this. 



Taking further into account the width of outcrop of the various 

 groups along the axis of the Corris Anticline, it would appear that, 

 between the outcrops of the perscuJptus zone and the prominent 

 grit-band on Mynydd Braich-goch, the average pitch is rather 

 more than 30° ; while between the grit-band and the Narrow Vein, 

 the average pitch cannot be more than from 16° to 18°. Farther 

 north along the axis the pitch would appear to be still less for 

 some distance. 



It is considered, therefore, that the amount of the pitch varies 

 considerably along the axis of the Corris Anticline, and it is 

 possible that this feature is repeated along the axes of the other 

 folds in the area. 



It will be observed, further, from an examination of the form 

 of the outcrop of the Narrow Vein in the Corris Anticline about 

 the Braich-goch Quarries, that there is fairly considerable torsion 

 of the anticlinal axis. The direction of axis as revealed by the 

 outcrops of the persculptus band and the grit-band mentioned 

 above, indicates a direction a few degrees east of north ; while for 

 some distance in the Braich-goch quarrying area the axis trends 

 distinctly west of north. Subsequently the axis veers to the east 

 of north again, as revealed by the location of the volcanic outcrop 

 on the north-western slopes of Mynydd y Waun. 



Q. J. G. S. No. 316. 2 o 



