part 2] PAL^^ozoic eocks or the llangollej^ district. 197 



Soatlieni Limb of the Llangollen Syiiclinorium. 



On the south side of the Llangollen Synclinorium the A^alentian 

 succession is even more obscure than in the north. The whole 

 group of rocks is much reduced in thickness, and is very unfossili- 

 ferous. 



Corwen-Moel-Fferna Area. 



In the Corwen-Moel-Fferna district the following appears to be 

 the sequence : — 



Wenlock. 



f Cyrtograptus- 

 \ mnrcliisoni Zone. 



Banded slates. 



( 



Upper Valentian 

 or T a r a n n o n. 



Lower Valentian) 



or Birkhillian. 



Ashg-illian. 



Dark, splintery, bine slate and 



banded slate. 

 Grey-green sandstone and slates, 

 with pebbles or nodules of 

 limestone in places. 

 M.-turriciilatus Striped and grey-green slates. 

 Zone. 



Dark mudstone yielding grapto- 



lites. 



Grey-green gritty slates, in places 

 speckled, and interbedded, es- 

 pecially near the base, with 

 thin sandstone -bands. 

 Cor wen Grit. 



? Monograx>tiis- 



crennlatus Zone 



? M.-crispus 



Zone. 



M.-convolutus 

 Zone. 



There is no apparent unconformit}^ at the base of the Valentian. 

 The convolutus zone was determined by Dr. Grroom & Mr. Lake ^ 

 in Nant-Llechog. Near the Corwen slate-mine, and at the head- 

 waters of the Ceiriog, forms were found by iis indicating the 

 tu7V'iculatus zone : — 



Climacograptus extrermis H. 



Lapworth. 

 Monogj'ajjtus tecki Barrande. 

 M. dextrorsHs Linnarsson. 

 M. exiguus Nicholson. 

 M. gemmatus Barrande. 

 M. priodon Bronn. X 



Monograptus inarri Perner. 



M. nudus Lapworth. 



M. pandtis Lapworth. 



M. runcinaUis Lapworth. 



M. hirriculatus Barrande. 



M. halli Barrande. 



Betiolites geinitzianus Barrande. 



1 



2 



X 



X 



X 



X 



X 



X 



X 



V 



X 



/'S 



X 



. 



X 



1 — Head- waters of the Ceiriog, south side of Moel-Fferna. 



2=In stream 330 yards north-west of the Corwen slate-mine, near Carrog. 



There is no great thickness of rock between the convoltitus and 

 the tnrriculatus zones, and no appearance of unconformity^ 



The Glyn-Ceiriog Area. 



In this area Dr. Groom & Mr. Lake's map and description of the 

 Valentian succession have been confirmed in the main. The con- 

 formable upward succession from the Grlyn Grit was proved by 

 them, and can be studied in quarries and natural exposures near 



Q. J. G. S. vol. slix (1893) pp. 432-33. 



