ANNIVERSARY ADDRESS OF THE PRESIDENT. 



II 9 



important bearing upon the distribution of the Graptolithina or 

 Rhabdophora, it being well known that in the Llandovery rocks of 

 Wales no Graptolites occur. The Lower Llandovery of Cardigan and 

 Merioneth, of such great thickness and extent (yet without Grap- 

 tolites), has " dwindled down to the thickness of the Birkhill Shales 

 (about 70 feet) in the intervening Lake- district, where it constitutes 

 the Coniston Mudstones — a group of beds almost identical in thick- 

 ness, lithology, and palaeontology with the equivalent Scottish deposit 

 of the Birkhill Shales" (Lapworth). ' The conclusion arrived at by 

 Mr. Lapworth, that the oldest beds of the south of Scotland (the 

 Glenkiln Shales) are the equivalents of the highest Llandeilo rocks, 

 is borne out through his researches amongst the Moffat series 

 in Southern Scotland ; and, with him, we must come " to the 

 conclusion that the Lower Silurian rocks of the southern uplands 

 can be arranged in two distinct formations, viz. a lower and very 

 thin group of fine-grained Graptolite shales, and an upper and com- 

 paratively massive series of arenaceous strata. In their mineralo- 

 gical features and palseontological characteristics the Moffat series 

 differ from any of the typical Silurian rocks of the principality." 

 Unlike the rocks of Wales, they are almost exclusively Graptolitic 

 in their fossil contents, scarcely any Brachiopoda or Crustacea being 

 known throughout the series. The Llandeilo age of the Lower 

 Moffat shales is further determined through the total absence of those 

 complex Arenig forms of " Dichogra/pti, Tetragrapti, and Phyllo- 

 grapti, so characteristic a feature of the Graptolitic fauna of the 

 Skiddaw, Shelve, St. David's, and Canadian equivalents." 



Mr. Lapworth, " arranging the Moffat strata in the order in 

 which they are displayed, and distinguishing each chief band by its 

 peculiar fossil," gives the following Table : — 



( Upper Birkhill 1 Zone of Bastrites peregrinus. \ 

 or Grey Shale I Zone of Monograptus spinigerus. 

 group. J Subzoneof Diplograptus cometa. | Lower 



Lower Birkhill 1 Zone of Monograptus grcgarius. \ Llandovery, 



or Black Shale I Zone of Diplograptus vesiculosus. 



J Zone of Diplograptus acuminatus. 



III. 



Birkhill 

 Shales. 



group 

 ( Upper Hartfelll 



II. 



Hartfell-j 

 Shales. ' 



I. 



Glenkiln 

 Shales. 



I Zone of Dicellograptus anceps. 

 Zone of Barren Mudstones. 



I 



}.Bala. 



orBarrenMud- 

 stone group. J 

 Lower Hartfell 1 Zone of Pleurograptus linearis. 



or Black Shale I Zone of Dicranograptus Cliwgani. \ 

 group. J Zone of Climacograptus Wilsoni. ) 



Ul Sh e a r ief eilklln } VMymograptus beds. 1 Upper 



L L0 S W haief 6nkiln } Ribbed ^stones. J I^eilo. 



The facies of the Glenkiln shales is distinctively that of the Llan- 

 deilo of South and North Wales, the assemblage being the same : 

 differences occur dependent upon locality and the mineral composition 

 of the beds ; but the common Glenkiln forms of Scotland, and those 

 species collected by observers in North Wales (Messrs. Salter, Hop- 

 kinson, Homfray, Gibbs, &c), serve at once to connect and correlate 

 the faunas of the two areas. 10 species from South Wales and 12 

 from North Wales are all Glenkiln species and of Llandeilo age ; 



Tc 2 



