372 MI6S G. L. ELLES ON THE WENLOCK [May I9OO, 



II. LlTEEATTJRE. 



The Builth District. 



Very little has been written about the Wenlock Shales of Builth, 

 though much attention has been paid to the Llandeilo Beds of that 

 area. The Wenlock Beds merely receive a passing mention in 

 Murchison's 'Silurian System' (1839) p. 315, and also in his 

 ' Siluria ' 5th ed. (1872) p. 59. In the last-named work, however, 

 sections are drawn across the Builth country, and the Wenlock 

 Beds are grouped together as a series of mudstones containing 

 graptolites and Orihoceras. A summary account of the Silurian 

 rocks of the Builth district is found in Mem. Geol. Surv. vol. i 

 (1846) p. 22, and the chief localities for fossils are recorded in 

 vol. ii, pt. i (1848) p. 327, etc. The only suggestion of their possible 

 division into zones is given by Lapworth in his ' Geological Distribu- 

 tion of the lihabdophora.' x He separates the zone of Cyrtograptus 

 Murchisoni from higher beds in which C. Linnarssoni is a character- 

 istic fossil. At the end of the same paper he also states his opinion 

 that the day will come when ' by the aid of the lowly graptolite the 

 geologist of the future will be able to read off the natural succession ' 

 in the monotonous Silurian mudstones of Britain with ease and 

 certainty. 



The Long Mountain. 



Prof. Watts has written two papers dealing with the Silurian 

 rocks of the Long Mountain. In the first of these, ' On the Igneous 

 & Associated Rocks of the Breidden Hills in East Montgomeryshire 

 & West Shropshire,' 2 he divides the Wenlock Shales of the area 

 into an upper and lower series. In a paper read before the British 

 Association in 1890 and subsequently published in abstract, 3 he 

 modifies his earlier views and considers that the beds represent the 

 upper part of the Wenlock Shale together with the Wenlock 

 Limestone. My own work confirms his later opinion. 



The Dee Valley. 



The Llangollen Basin has been studied by many geologists. 

 The most important recent paper is one by Mr. Lake on ' The 

 Denbighshire Series of South Denbighshire.' 4 This paper contains 

 a summary of the earlier work on the beds exposed in the area, 

 and the author divides the Wenlock Beds of the district as 

 follows : — 



Moel Fern a Slates, with M. Flemingii and M. priodon. 



Pen-y-glog Grit. 



Pen-y-glog Slates, with M. personatus, M. priodon, etc. 



1 Ann. & Mag. Nat. Hist. ser. 5, vol. vi (1880) p. 201. 



2 Quart. Journ. Geol. Soc. vol. xli (1885) p. 532. 



3 Rep. Brit. Assoc. 1890 (Leeds) p. 817. 



4 Quart. Journ. Geol. Soc. vol. Ii (1895) p. 9. 



