150 PEOF. 0. T. JONES OX [vol. Ixxvii, 



inclined, on the ground of their pM^sical relations, to class them 

 with the Wenlock ; while Salter maintained that their palseon- 

 tological affinities were with the Upper Llandover}'. 



Murchison^ regarded them as occupying an intermediate jwsition 

 connecting the Lower Avith the Upper Silurian rocks. On account 

 of the unsettled status of this group, it became customar}^ to use 

 the term Llandoverv-Tarannon in referrins^ to the rocks 

 between the Bala or Caradoc and the Wenlock. 



In 1875 T. McKenny Hughes ^ suggested that the base of the 

 Silurian of Sedgwick (Upper Silurian of Murchison) should 

 be drawn, not between the Upper and Lower Llandovery, but at 

 the base of the latter, and he proposed the name May -Hill 

 Series to include the L^pper and Lower Llandover}- and the 

 Tarannon, This was adopted by H. B. Woodward in his ' Geology 

 of England & Wales,' where these rocks are arranged as follows : — 



r Tarannon Shales. 



May-Hill Series < Upper Llandovery. 



[ Lower Llandovery. 



It is doubtful whether the extension of the name Ma}" Hill to 

 include the Lower Llandovery rocks is justifiable, since there is no 

 evidence of this group in the type-district of May Hill. 



The proposal to include the Lower Llandovery in the Upper 

 Silurian which had been urged, also, by Lyell, Hicks, and others, 

 was destined to receive su})port about two years later from an 

 unexpected quarter. In 1878 was published Charles Lapworth's 

 remarkable paper on ' The Moffat Series,' ^ wherein he compares 

 the three divisions (Glenkiln, Hartfell, and Birkhill) there 

 established with the three successive formations Llandeilo, Bala, or 

 Caradoc, and Llandovery of Siluria. The correlation of the two 

 lowermost divisions was based on a comparison of the graptolite 

 species which were known to be common to the Scottish and the 

 Welsh deposits, or their undoubted foreign equivalents ; but, as not 



* a single species of the Birkhill fauna ' had at that time been 



* recorded from any of the Silurians of the Principalit}',' he was 

 unable to make a direct correlation based on community of sjDecies. 



The Coniston mudstones were, however, known to occupy a 

 position above the equivalents of the Bala Limestone, and were 

 crowded with typical Birkhill forms. Also, identical species had 

 been recorded from the Kieselschiefer of Thuringia, which were 

 placed by Murchison and others at the junction of the Lower and 

 the Upper Silurian, while they were known to occur in the Upper 

 Graptolite Shales of Sweden, which overlie everything to which 

 the name Bala could be applied. From these considerations 

 Lapworth was able to affirm that the Birkhill shales were of Lower 

 Llandovery age. Two years later he followed up this paper by a 

 remarkable series of papers on ' The Geological Distribution of the 

 Rhabdophora ' ^ in which he brings together all the information 



1 ' Siluria' 5th ed. (1872) p. 103. 



2 Eep. Brit. Assoc. (Bristol) 1875, Trans, p. 70. 



3 Q. J. G. S. vol. xxxiv (1878) p. 240. 



^ Ann. Mag. Nat. Hist. ser. 5. vol iii (1879) p. 455 & vol. v (1880) p. 45. 



