1843.] 257 



between Llangynog and Eala, dipping westward beneath the chain 

 of the southei'n Berwyns. 



Below the village of Llanwddyn there continues a prevailing 

 westerly dip ; but the derangements are enormous, and, at the 

 great bend in the Fyrnwy river, the lower Silurian rocks {g) are 

 seen resting upon the upper (Ji) in a reversed position. 



In this section, as in the former, the protozoic series is of great 

 thickness. 



Skction III. 



AaRAN MoWI)J;y to Lr-ANLIHANGEL. 



Direction of the Section, W. 10° N. to E. 10° S. 

 Horizontal base 1 7 miles. 



This section commences with cotemporaneous porphyries 

 {a a') ; but they break out at a still higher geological level than 

 in Section II. The porphyry is succeeded by grey slates {b b'') 

 containing the Bala series {b ), which may be followed southward 

 in the direction of the strike, down the western bank of the Dyfi. 

 The beds dip east by south, except to the extent of a faulted in- 

 terval (c) on the east side of Carreg-y-big. "We have in this line 

 of section a great thickness of the fossiliferous portions of the 

 protozoic series, but not the whole thickness ; since these beds are 

 succeeded in the line of section by a trough of overlying and un- 

 conformable Upper Silurian rocks, dd\ These rocks accord with 

 the type, not of the Denbigh or Montgomery flagstones, but of the 

 coarse-grained greywacke and flagstone which form the base of 

 the upper system near Cernioge. 



Beyond this trough, the older beds (e e') again rise out, but with 

 a reversed or northwesterly dip, and at a very high angle of incli- 

 nation. At the east end of this, as of the former section, the Upper 

 Silurians (/) pass under the Lower (e), owing to inversion. 



In following the fossiliferous beds of the southern Berwyns to 

 the neighbourhood of Mallwydd, the author found those beds over- 

 laid by Upper Silurian rocks of the Cernioge type ; a fact which 

 had previously been noticed by Mr. Sharpe. Mr. Sharpe, how- 

 ever, considers that these Upper Silurians rest conformably on the 

 Lower, and that the entire upper part of the Lower system is here 

 displayed. * The author considers that the upper system wraps 

 round the southern end of the Berwyns unconformably ; and that 

 the upper part of the lower system is incomplete, f 



• Proceedings of the Geological Society, vol. iv. p. 13, 



+ The errors committed in certain parts of Mr. Murchison's map, in the 

 neighbourhood of Mallwydd, by spreading the Cambrian colour over an area 



