ANNIVERSARY ADDRESS OF THE PRESIDENT. 151 



Tortworth, in many localities in Shropshire (Norburj 7- , Chcrbury, 

 Church Stretton, &c), and at Llandovery, Prosteign, &c. in South 

 Wales, the Upper Llandovery or May-Hill beds are typically exposed. 



Many names have been proposed for these variable beds, such as 

 Upper Caradoc, Pentamerus-heds, Wcnlock Grit, &c. ; but, through 

 their chief development at Llandovery and May Hill, in Gloucester- 

 shire, the double name of the " Upper Llandovery," or " May -Hill 

 Sandstone," has been given to them. In North Wales the Upper 

 Llandovery rocks are absent ; in South Wales they first appear in 

 Marloes Bay, appearing here and there across Pembrokeshire. Near 

 Llandeilo, in Caermarthenshire, they lie at the base of the Upper 

 Silurian rocks, being most variable in thickness. They transgress 

 or lie indifferently and unconformably on Lower Llandovery, Caradoc, 

 or Llandeilo beds. In Shropshire they are markedly unconformable 

 to the Caradoc. In the Longmynd area, under the condition of a 

 calcareous conglomerate, they rest upon all the older rocks exposed. 

 That a great physical break takes place between the two Llandoveries 

 there can be no doubt. They rise from under the W enlock Shale at 

 Noeth Grug, strike to near Llandovery and Pen-y-lan ; again they 

 range uninterruptedly from Marloes Bay, in Pembrokeshire, where 

 they are highly fossiliferous (28 species occurring there), through 

 Caermarthenshire to Builth, and on to the Longmynd and typical 

 Silurian country of Shropshire. They everywhere rest unconform- 

 ably upon the older rocks, sometimes lying on the denuded edges of 

 the Lower Llandovery or on the Caradoc Sandstone ; at Builth and 

 the Longmynd on the contorted and denuded Arenig, Llandeilo, and 

 Cambrian strata. 



The absolute unconformity of the Upper Llandovery beds to the 

 strata below, coupled as it is with changes of species, is doubtless 

 connected with a lapse of unrepresented time. Whether that time 

 be of great duration or not we have no means of judging ; but, 

 looking at the intimate connexion between the fauna of the Lower 

 Llandovery and that of the Upper, we are led to suppose that it 

 was not of sufficiently long duration to cause either the extinction 

 or migration of the older fauna or the introduction of a new one 

 (only 4 genera seem to have appeared) ; for we have seen that the 

 Lower Llandovery transmitted 45 genera and 104 species, out of 

 its fauna of 68 genera and 204 species, to the Upper Llandovery. 

 It is therefore evident that upheaval and denudation must have 

 been of comparatively short duration, and little physical change 

 could have taken place in the area occupied by the Lower Llan- 

 dovery after upheaval ; this the physical geography and palaeontology 

 of the two groups help to show. 



The preponderance of individuals in species of the genera Penta- 

 merus and StricJdandinia, especially P. oblongus, S. lens, and S. lirata, 

 which are the best known and most widely spread, is a marked 

 feature in the Upper Llandovery rocks, and imparts to them peculiar 

 and distinct facies. These species occur, though not so plentifully, 

 in the Lower Llandovery. The Malvern and May-Hill form is 

 8. lens, and it occurs in profusion. Looking at the grouping of the 



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