The Crystalline Limestones of Ceylon. I'll 



2. ' On the Origin of the River- System of South Wales, and its 

 Connection with that of the Severn and Thames." By Aubrey 

 Strahan, Esq., M.A., F.G.S. 



The southerly courses of some rivers from the Usk to the Ogmore 

 are described, and shown to be independent of both the east-and- 

 west folding and the north-north-westerly faulting of the rocks 

 on which they lie. Farther west the drainage-system takes a 

 different direction, the rivers coinciding so closely with a set of 

 west-south-westerly disturbances as obviously to have been deter- 

 mined in direction by them. 



Of the three systems of disturbance alluded to, the east-and- 

 west (Armorican) folding was pre-Triassic ; it marks a period of 

 compression with impulse from the south, and though it reached 

 great intensity in Devon, Somerset, and South Wales, it died away 

 in Central AY ales. The north-north-westerly (Charnian) faulting, 

 though partly of pre-Triassic age, was renewed in post-Eocene times,, 

 and is manifested over much of the British Isles. It marked periods 

 of relief from pressure, and of subsidence. The west-south-westerly 

 (Caledonian) folding was the latest ; it marked a period of com- 

 pression, with impulse from the north, and displayed greater energy 

 in Central than in South Wales. It gave rise to a series of sub- 

 sidiary disturbances in the latter region, and initiated and controlled 

 the river-system. The ignoring by the rivers of the structures due 

 to the earlier disturbances is attributed to the Palaeozoic areas having 

 been overspread by Upper Cretaceous rocks at the time of the 

 initiation of the river-system. 



The eastward course of the Upper Severn is attributed to the 

 upheaval of a main axis (now the main water-parting) in Central 

 Wales. Its deflection to the south and south-west was due to the 

 formation of an anticline in the Chalk, which must have been 

 parallel to, but a little west of, the present Chalk-escarpment, and 

 which was parallel to, and contemporaneous with, the Caledonian 

 disturbances in Wales. 



This anticline, acting in combination with the Armorican folding 

 displayed in the London and Hampshire basins initiated the systems 

 of the Thames aud Erorae. Those systems were initiated in post- 

 Oligocene and pre-Pliocene times, and the same age is inferred for 

 the systems of South Wales and of the Severn. 



March 12th.— Sir Archibald Geikie, D.C.L., LL.D., F.U.S., 

 Vice-President, in the Chair. 

 The following communications were read : — 

 1. ' The Crystalline Limestones of Ceylon.' By Ananda K. 

 Coomaraswamy, Esq., B.Sc, F.L.S., F.G.S. 



The crystalline rocks of Ceylon may be divided iuto three 

 series : — 



(1) The Older Gneisses. 



(2) The Crystalline Limestones. 



(3; The Grranulites (C harnockite Series) — pyroxene-granulite, 

 leptynite. etc. A local subdivision of this series is the Point de- 

 Galle Group— wollastonite-scapolite-gneisses, etc. 



