370 MISS G. L. ELLES ON THE WENLOCK [May I9OO, 



23. The Zonal Classification of the Wenlock Shales of the 

 Welsh Borderland. By Miss Gertrude L. Elles, of 

 Newnham College. (Communicated by J. E. Marr, Esq., 

 M.A., F.B.S. Bead December 20th, 1899.) 



[Plate XXIY.] 



Contents. 



Page 



I. Introduction 370 



II. Literature 372 



III. The Builth District. (Map on p. 385.) 373 



IV. The Long Mountain District. (Map on p. 395.) 386 



V. The Dee Valley 397 



VI. General Conclusions and Correlation 401 



VII. Palaeontology 401 



I. Introduction. 



In Southern Sweden occurs a series of shales of Wenlock age, 

 which Tullberg divided into zones by means of their predominant 

 graptolites. 1 During a visit to that country in the early part of 1896, 

 I was enabled, through Dr. Tornquist's kindness, to spend some time 

 in studying the fauna of these zones, and I determined that when I 

 returned to England I would ascertain whether some such zonal 

 classification did not also hold good for the beds of Wenlock age in 

 our own country. 



During the past four years I have studied in detail the strata 

 and the graptolites of the Wenlock Beds of the Welsh Borderland, 

 and I find that such a classification can certainly be made. Further, 

 as the existence of Tullberg's zones 2 has recently been called in 

 question, and doubt has been thrown upon the validity of several 

 of his species, it seems only fair to the memory of that geologist to- 

 bring forward the results that I have obtained, which appear to me 

 to confirm his work completely. 



A glance at the Geological Survey maps of the Welsh Borderland 

 would seem to indicate that the Wenlock Shales cover a consider- 

 able extent of country. This, however, is not really the case : far 

 from being of wide extent, the Wenlock Shales are generally present 

 as a mere fringe below the Ludlow rocks. It is the Ludlows, 

 and particularly the Lower Ludlows, which occupy the greater 

 part of the area. Frequently the so-called ' Ludlow ' of the 

 Geological Survey maps of the Welsh Borderland is the equivalent 

 of the Upper Ludlow of the maps of the typical area of Shropshire. 

 The reason for this seems to be, that the Wenlock Shales and 

 Lower Ludlow Beds of the Welsh Borderland are often identical in 



1 « Skanes Graptoliter ' pt. i (1882) Sver. Geol. Undersokn. ser. C, no. 50, 

 p. 15. 



3 Freeh & Roemer, « Lethsea Palaeozoica ' vol. i, pt. iii (1897) pp. 650-653. 



