OX THE GEOLOGY OF CENTRAL WALES. 141 



12. The Geology of Central "Wales. By Walter Keeping, Esq., 

 M.A., E.G.S., Lecturer on Geology in the University of Cam- 

 bridge. With an Appendix on some neiv Species of Cladophora, 

 by Charles Lapworth, Esq., E.G.S. (Read June 23, 1880.) 



[Plate VII.] 



Contents. 



Part I. 



Introduction and Historical. 

 Illustrative section from Aberystwyth 



to the Devil's Bridge and Plyn- 



limrnon. 



(1) The Aberystwyth Grits. 



(2) The Metalliferous-slate Group. 



(3) The Plynlinimon Group. 



Part H. 



Brief notes upon other sections. 



(1) Aberystwyth through Pont 



Erwyd to Builth. 



(2) Llandeilo to Aberaeron. 



(3) Ehyader to the Teifi Pools. 

 General results. 



More distant sections. 



(1) Llanbrynmaer area. 



(2) Dovey-valley area. 



(3) Corris area. 



(4) The Cardigan area. 

 General results. 



Part III. 



Palasontological evidence. 

 General summary. 



Appendix. 



Appendix by Mr. C. Lapworth, F.G.S., 

 on new Species of Cladophora. 



Part I. 



The following communication contains some of the results worked 

 out in frequent field-excursions during three years' stay at the 

 University College of Wales, Aberystwyth. In many of these ex- 

 cursions I was accompanied by my students of the College ; and to 

 them I am indebted for much help both in the museum and the 

 field*. Our principal field of work was, naturally, within a radius 

 of some fifteen to twenty miles around the town of Aberystwyth ; 

 and most of this country we have carefully searched and traversed 

 through and through. The more distant areas to the south of 

 Cader Idris, at Llanbrynmaer, Llandovery, Llandeilo, Cardigan, &c, 

 have also been visited with a view to the determination of the 

 extent and variation of the Cardiganshire rock-groups, and the dis- 

 covery of their stratigraphical relations to other and better-known 

 geological horizons. 



Little has yet been done by geologists to elucidate the structure 

 of this part of Wales : while the most careful labours of our greatest 

 authorities have been devoted to the study of the northern counties 

 and eastern borders of Wales, and also, of late years, to the south in 

 Pembrokeshire, this barren and chaotic area of Mid Wales has been 

 always neglected, and is even now very rarely touched with the geolo- 

 gical hammer. Eor the bibliography of our subject we have therefore 

 but little to say, the most important contributions being : — the work 



* In particular, I have received much assistance from my former pupils 

 Mr. T. Roberts, now of St. John's College, and Mr. E. Evans of Sidney College, 

 Cambridge. 



