Vol. 56.] WENLOCK SHALES OF THE WELSH BORDERLAND. 401 



YI. General Conclusions, and Correlation of the Beds of the 

 Welsh Borderland with their Foreign Equivalents. 



"We have now completed our examination of the arrangement of 

 the strata and the distribution of the graptolites in three of the 

 most important areas of Wenlock rocks in the Welsh Borderland, 

 namely, the Builth District, the Long Mountain, and the Dee 

 Valley. The beds are not equally developed in the three areas ; the 

 succession is most complete at Builth, but the upper beds are best 

 developed in the Long Mountain, and the relationship of the 

 lowest beds is clearest in the Dee Valley. In all three cases, 

 however, the lithological and pakeontological evidence is in full 

 accord. 



The various species of graptolites which are met with in the 

 strata of each area group themselves into an ascending succession 

 of recognizable graptolilic sub-faunas, which in all three districts 

 are the same. It must therefore, I think, be admitted that the 

 Wenlock Shales of the Welsh Borderland, like those of Southern 

 Sweden, are capable of a zonal classification, using the characteristic 

 graptolites as zone-indices. The accompanying table (VJ.I.1, p. 400) 

 indicates the zones present in each area and their correlation with 

 the beds in Southern Sweden. 



The two lowest zones of the Welsh Borderland and the highest 

 are apparently present in Bohemia also, for I have collected the 

 typical fossils there, although I am not aware that detailed mapping 

 or the zones has yet been done for that country. In Sweden and 

 Bohemia the typical fossil of the highest beds is Monograptus testis, 

 but in our own country the most widespread form is certainly Cyrto- 

 yraptus Landgreni, and therefore I have chosen it for my zone-fossil. 

 The true M. testis of Barrande has not yet been recorded in this 

 country. Cyrtograptus Carruthersi, which is used by Tullberg as a 

 zone-fossil, is not very abundant, and is liable to be confused 

 with Mo nog rapt as Nilssoni of the Lower Ludlow. 



VII. Paleontology. 



The graptolite-fauna of the Wenlock Shales is rather monotonous ; 

 in all, there are not more than four genera represented, and the 

 number of species (including varieties) does not exceed thirty. 



The Cyrtograpli attain their maximum development in these 

 beds, though they are certainly found in lower beds, and one 

 species perhaps passes up into the Lower Ludlow. The Monograpti 

 are also abundant, though the number of species represented is far less 

 numerous than in the earlier horizons. Several Continental forms 

 already recognized in Sweden are here recorded from this country, 

 tor the first time ; with regard to others previously recorded 

 as occurring in Britain, some notes are necessary. A few new 

 species have been obtained, and these are described in detail. 



