1843,] 265 



Section VIII. 



From the Teirw River, across the valley of the Dee, to Cricor Mawr, neaar 



the head of the Vale of the Clwyd. 



Mean, direction of the line of section, S. 20° E. to N. 20'' W, 



Horizontal base 11 J miles. 



W. 30° W. S. 30° E. N. 5° W. S. 5° E. 



f Ci-icor Ma%vr. Moel y Gamelyn. q Glyn Ceiriog. S 



b X' 



This Section is nearly the counterpart of Section VIL, and runs 

 nearly parallel to it : it passes the Dee about 3 miles W. of Llan- 

 gollen. At the southern extremity, on the Teirw river, we have the 

 limestones (X X"), and porphyries (tt) of the Palseozoic series (a). 

 Then follows a trough containing the dark roofing slate and 

 the flags (b b'), of the upper Silurian series. Towards the 

 northern extremity of the trough, a mass of the older rocks {c\ 

 abounding, like the similar mass of Cyrn-y-brain, in fossils of the 

 Caradoc sandstone, breaks out at Cricor Mawr. This mass is 

 covered, on its north-western flank, by upper Silurian rocks ; and 

 these are overlaid by mountain limestone {d), a range of which 

 bounding the vale of Clwydd on the S. E. runs from the point 

 represented in the Section, beyond Abergele. The mountain lime- 

 stone is followed by new red sandstone (/), 



Section IX. 



From Garn Brys, S. W. of Cernioge, to Abergele, 



Hbrizotittil base 20 miles. 



<i b a' b' c" d e f g 



In this Section, we have, near Cernioge, first, the rocks of the 

 older series («), abounding with fossils of the Caradoc sandstone ; 

 and secondly, lying unconformably on the preceding, are the con- 

 glomerates and sandstones {b) which there constitute the base of 

 the upper Silurian series. These conglomerates, &c., the author 

 compares to the coarse greywacke and flagstone which constitute 

 the unconformable base of the upper series at the south-eastern 

 extremity of the Berwyns. These coarse mechanical rocks do not 

 appear in any distinct form in the country traversed by the two 

 former lines of section. The conglomerates pass into sandstones 

 (c') of a finer structure, which alternate with bands of dark coaree 



X 2 



