204 DR. WILLS AVD AIE. SMITH 0>'' THE LO^EE [vol. Ixxviii, 



fossils are not so easilr studied. The following appears to be the 

 succession : — 



ThicJcness in feet. 

 Slates and silty sandstones of Lower Ludlow tyx>e- 

 Gritty blue slates, with occasional trilobites and Orthoceras r 100 

 ' Bastard ' banded slates, with a 20-foot bed. near the base, 

 composed of brecciated blocks of laminated shale set in 



a bine shaly matrix, the whole being well cleaved r 250 



Banded roofing-slates, with beds of spar r 60 



Banded mndstone, yielding fossils of the Cyrtograptus- 



murchisoni Zone r 15 to 20 



The brecciated bed mentioned above niav be seen in an old 

 cjuaiTv near Cae"r-hafod. and also near Ty-cerrig. The blocks of 

 shale composing it are disposed in every direction, as revealed by 

 the lamination ; but the normal cleavage goes through all, Avithout 

 reference to the orientation of the blocks. The band provides 

 evidence of considei-able consolidation of the silts and muds soon 

 after their deposition — in fact, before the laying-down of the 

 succeeding beds of shale. Brecciation within a bed the upper and 

 lower surfaces of which are sub-parallel, and possess the same dip as 

 the neighbouring rocks, seems to point to penecontemporaneous 

 disturbance, perhaps by an earthquake, on similar lines to those 

 suggested by Prof. P. F. KendalL- 



In the Brvneglwys area, the Wenlock deposits are blue and 

 banded slates : but, as they have not been exploited, little can be 

 made out of the detailed succession. The Cy/'tograpfus-nuirclusoni 

 Zone, however, has been detected at points near the Tarannon-Slate 

 outcrops. The structure of this area is dealt with on p. 211. 



(3) Lower Ludlow Series. 



{a) Th- Ludlow Series in the Llangollen Synclinorium. 



(ij Glyu-Dyfrdwy G-roup, — In the southern part of the 

 synchnorium there is no lithological feature and practically no 

 palseontological evidence on which to draw the base of the liower 

 Ludlow Series. It is probable that the bortom part of the Glvn- 

 Dyfi'dwy Group is absent through faulting in the Glvn-Ceiriog 

 valley : and, if present farther west, it is poorly exposed on the 

 moors. Xear Carrog and Moel-Ff erna the normal upward sequence 

 from the Pen-y-glog Grit appears to be inten-upted by a north- 

 and-south fault along the Xant Ffridd-isel, which cuts out the 

 basal part of the group. 



Could we but study this basal member adequately, it would 

 probably be found to fall in the zone of Man og rapt us vulgaris 

 which Dame Ethel Shakespear believed that she could recognize in 



1 Abs. Proc. G^eol. Soc. 1918-19, p. 28 : see also B. Smith, GeoLMag. 1916, 



pp. T4i>-o6. 



