524 



JONES ON THE HARTEELL-VALENTIAST [Nov. I909, 



clearly seen on the ground, the nature of the structure is obvious 

 (see fig. 15, p. 523). In the absence of clear exposures, however, 

 a normal fault would seem the most natural explanation. What 

 is probably the same folded belt is visible in the lower strata of 

 the Pont Erwyd Stage, in the Rheidol near Craignant-mawr. 

 The remarkable variation in the width of an outcrop in different 

 parts is another consequence 

 71 of the folding of the rocks. 

 \ Thus, at Eistedrlfa Gurig, the 

 ' Eisteddfa and Kheidol Groups 

 I are contained in a width of 

 g 350 yards ; while about a mile 

 I to the south the same strata 

 * occupy more than five times 

 that width, although this is 



1 partly accounted for by the 

 = form of the ground. A com- 



2 parison of fig. 3 with fig. 4 



3 (p. 476) will make it clear how 

 H this difference arises. 



With regard to the indivi- 

 | duai folds, it may be doubted 

 h whether they persist far in 

 _; either direction. On com- 

 -, paring the two sections just 

 "- mentioned it will be seen that 

 | the deep syncline in Nant 

 § Nod has been replaced in a 

 k „ distance of about a mile by 

 2 a very shallow synclinorium, 

 - while the complementary an- 

 7. ticline in Afon Tarenig can 

 j scarcely be recognized. 

 = Again, on following the 



-i anticline which brings up the 

 II Eheidol Group on the south 

 c side of the Castell Fault south 

 2 of Euches-gau, the crest may 

 | be seen to flatten gradually 

 «r in a southerly direction until 

 | finally a syncline develops on 

 '£j that line, while a low anticline 

 arises on the east and another 

 on the west. If fig. 12 (p. 508) be examined, a shallow anti- 

 clinorium will be observed on Mynydd-yr-Ychion, composed of a 

 well-marked syncline bounded on each side by a sharp anticline. 

 This structure lies exactly in the range of the structure just 

 mentioned, and probably represents it in a more advanced stage, 

 but it still retains its anticlinal character. 



