Ludlow. 



{ 



Wenlock 

 Shales. 



Reports and Proceedings — Geological Society of London. 91 



north and north-west of beds which are overlapped to the east. The 

 full six zones in the foregoing table occur to the north-east of 

 Builth Eoad Station, but some of them are overlapped north-west of 

 Builth; and at Aberedw Hill, east of Builth, only the highest zone 

 is exposed. The entire succession in the north and north-west part 

 of the district is given below : — 



10. Hard light-grey siliceous flags. 

 9. Micaceous sandy shales, with rotten limestone bands. 

 ( 8. Calcareous flagstones, with fossiliferous bands. 

 (/) 7. Calcareous fissile shales, with beds of flagstone. 



= Zone of CyrtograpUis Lundgreni. 

 (e) 6. Hard grey calcareous shales with graptolites. 

 = Zone of Cyrtograptus rigidus. 



5. Light-coloured flags, unfossiliferous (400 feet) ? 



(d) 4. Grey calcareous flags and shales, with limestone 



concretions 300 feet. 



= Zone of CyrtograpUis Linnarssoni. 



(r) 3. Soft shales with harder flaggy beds 200 feet. 



= Zone of Cyrtograptus, sj). nov. 



{b) 2. Hard calcareous flagstones 300 feet. 



= Zone of Monograptus Riccartoncnsis. 

 («) 1. Soft fissile shales alternating with flags. 



= Zone of Cyrtograptus Murchisoni. 



The Wenlock Shale of this area was deposited on the sinking 

 shore-line of the old Llandeilo ridge, resulting in the overlap of 

 higher beds on lower. 



The Long Mountain is a syncline with north-east and south-west 

 axis. Here also there must have been deposition on a sinking ridge 

 accompanied by overlap. The lowest beds, exposed near Chirbury, 

 belong to the zone of Monograptus Riccartonensis ; but on the 

 north-west side, near Middletown, the lowest beds seen above the 

 Tarannon shales belong to the zone of Cyrtograptus Linnarssoni. 

 The relationship of these beds to the Tarannon shales is regarded 

 as an unconformability. The sections in this district confirm those 

 established for the Builth area. 



In the Llangollen Basin the general structure is a synclinal fold 

 complicated by many minor folds and faults. The ' pale slates * 

 are covered by darker shales belonging to the zone of Cyrtograptus 

 Murchisoni ; and in this district the relationship of the lowest zones 

 is clearer than at Builth or the Long Mountain. 



The palaeontological part of the paper describes several species, 

 some of which are recorded for the first time in the country : 

 Cyrtograptus Carruthersi, C. rigidus, and a new species of Cyrto- 

 graptus of zonal value, four varieties of Monograptus Flemingii, 

 three of M. vomerinus, one variety of M. testis, and two new species 

 of Monograptus are amongst the forms dealt with. 



3. '• On an Litrusion of Diabase into Permo-Cai'boniferous Eocks 

 at Frederick Henry Bay (Tasmania)." By T. Stephens, Esq., M.A., 

 F.G.S. 



The relationship of the abundant diabase to the Permo-Carboni- 

 ferous strata of the island has been long a matter of dispute. 

 Among others, Jukes described sections which appeared to confirm 

 the view that Permo-Carboniferous sediments were deposited round 



