Reports and Proceedings — Geological Society of London. 331 



complicated by minor folds, faulting, thrusting, and crushing. The 



succession on the northern limb of the anticline is as follows ; — 



Bala-Caradoc. 



• Llandeilo. ( mcranogmptus Beds 



( Asaplms tyrannus Beds. 



Llanvirn \ Bidymograptus Murchisoni Beds. 



( Didymograptus bijidus Beds. 

 Arenig. Tetragraptus Beds. 



The succession on the southern limb is similar, but passes up into 

 higher beds, as shown below : — 

 Lower Llandovery. 



iSlade Beds. 

 Redliill Beds. 

 Sholeshook Beds. 

 Eobeston Watheu Limestone. 

 Llandeilo, Llanvirn, and Arenig as above. 

 The crushing and fracturing of the rocks have brought together 

 into a small area facies of rocks diifering lithologically and in 

 faunas, the difference being well shown in corresponding beds on 

 opposite sides of the anticline. The majority of faults are strike- 

 faults, many of them being thrusts ; these are sometimes so close 

 together that the structure cannot be fully displayed on the 1 inch 

 scale. Cleavage affects the rocks on the northern limb, but is 

 almost absent on the south; it was induced at a later date than 

 the faulting. The chief igneous rocks are intrusions of diabase ;. 

 and there are ashes in the Llanvirn and Llandeilo Beds and an ashy 

 shale in the Arenig. 



A description of the entire succession of rocks is given, accom- 

 panied by lists of fossils, and each division of importance is followed 

 through its whole extent as shown in the area. In correlating the 

 rocks, it is shown that the Middle and Upper Arenig rocks compare 

 with those of St. Davids ; the Llanvirn rocks are very similar, 

 lithologically, to the beds of Llanvirn and Abereiddy, and the faunas 

 are practically identical ; the Llandeilo rocks are in the main like 

 those of Pembrokeshire, but the Zeptograptus division of the 

 Dicranograptus Beds closely resembles the Rorx'ington Flags of 

 Shropshire ; the Bala-Caradoc rocks fall into the divisions already 

 established by Marr & Eoberts in an adjoining area ; and the rocks 

 assigned to the Lower Llandovery are barren of organic remains, as 

 they are elsewhere. 



IL— May 23rd, 1906.— R. S. Herries, M.A., Vice-President, in the 

 Chair. The following communications were read : — 



1. '•' On the importance of Ilalimeda as a Keef-forming Organism ;. 

 with a description of the Halimeda Limestones of the New Hebrides." 

 By Frederick Chapman, A.L.S., F.R.M.S., and Douglas Mawson, 

 B.E., B.Sc. (Communicated by Prof. T. \V. Edgeworth David,. 

 B.A., F.R.S., F.G.S.) 



Calcareous algse, nullipores, Lithothamnion, etc., have been fre- 

 quently referred to as forming important contributions to the rock 



