Yol. 67.] THE LLANDOVERY ROCKS OE MONTGOMERYSHIRE. 415 



15. The Llandovery and Associated Roexs of North -Eastern 

 Montgomeryshire. 1 By Arthur Wade, B.Sc, F.G.S. (Read 

 April 26th, 1911.) 



[Plates XXXIII-XXXVL] 



Contents. 



Page 



I. Introduction 415 



II. Historical Eeview 415 



III. Stratigraphical Literature 418 



IV. The Stratigraphical Succession 418 



V. Detailed Description of the Subdivisions 422 



VI. Structure of the Area 442 



VII. Correlation of the Strata 444 



VIII. Igneous Kocks— The Welshpool Dyke 446 



IX. Notes on the Palaeontology of the Area 449 



I. Introduction. 



The district investigated is one which was well loved by 

 Murchison, who paid many visits, about the year 1836, to Powis 

 Castle while preparing his great work on the ' Silurian System.' 



It extends for a distance of over 7 miles in a north-easterly 

 direction from a point a mile or so south of Welshpool in Mont- 

 gomeryshire, and includes a tract of country embracing the Yale of 

 Guilsneld, and a portion of the valley of the Severn. It is bounded 

 on the west by the watershed of the Vyrnwy, the area covering 

 nearly 40 square miles. The country may be broadly described as 

 consisting of three parallel ridges of Silurian rocks running in a 

 north-north-easterly direction, with two wide intervening valleys 

 containing subsidiary though usually more precipitous ridges, formed 

 by the escarpments of rocks of Ordovician age. It was among 

 these fertile valleys and finely wooded hills that De Quincy found 

 solace during part of his early wanderings. 



II. Historical Eeview. 



Murchison, ia 1839, was the first to give any account of the 

 structure of this region. Speaking of the whole of the country 

 between the Breiddens and the Berwyns, he describes [1] 2 the 

 Silurian strata as lying 



' in undulations or troughs constituting a number of parallel 



anticlinal and synclinal lines.' (Ch. xxiv, pp. 300 et seqq.) 



1 Thesis approved for the Degree of Doctor in Science in the University of 

 London. 



2 Numerals in square brackets refer to the Bibliography (§ III) on p. 418. 





