ANNIVERSARY ADDRESS OF THE PRESIDENT. I4I 



the Palaeozoic rocks. Only one species (Orthoceras arcvoliratum, 

 Hall) is common to the Caradoc and Llandeilo ; but 15 species 

 range upwards — 7 to the Lower Llandovery, 9 to the Upper Llan- 

 dovery, 4 to the Woolhope, 9 to the Wenlock, and 3 to the Ludlow ; 

 or the 15 make their appearance or occur 32 times in their range 

 through the higher divisions of the Silurian rocks ; 32 species are 

 therefore essentially Caradoc or Bala forms. The numerical distri- 

 bution of the Caradoc species through North and South Wales is re- 

 markably uniform. 12 species occur in the four North-Welsh coun- 

 ties, and 8 in the two South-Wales counties. Shropshire possesses 

 no Cephalopod, yet 57 genera and 123 species range through 13 

 zoological classes occurring in that county ; but even this number 

 represents numerically only a little over 2 species for each genus. 



Table X. is prepared on geographical data, the universality 

 or extension of the Caradoc rocks and species not admitting of 

 any other mode of expressing their distribution ; and to analyze 

 the group under subdivisions of the Caradoc or Bala, as given by 

 various authors, would end in confusion, owing to the application 

 of the terms Lower, Middle, and Upper Caradoc, or Bala, not being 

 the same in all. Text-books ha^e not yet denned the limits of these 

 divisions, either zoologically or geographically ; in the former sense 

 the greatest difficulty would be felt over extended areas, through 

 want of true succession and continuity in strike. A careful study 

 of the Woodwardian Catalogue demonstrates the difficulty of treating 

 the Caradoc or Bala group as a whole in any other way. The 

 column headed "Localities and Numbers" in that Catalogue at once 

 shows that it is only through space distribution that we can realize 

 the value of the subdivision. In the Lower Bala group of the Upper 

 Cambrian, as established by Sedgwick, Mr. Salter has placed 45 

 genera and 82 species; in the Middle Bala 82 genera and 212 

 species ; and in the Upper Bala group 43 genera and 100 species. 

 That the fossils of the " Lower Bala " of the Woodwardian Cata- 

 logue represent the Llandeilo proper of the Geological Survey there 

 can be no doubt ; and out of the 82 species catalogued, only 17 pass 

 to the Middle Bala group, and 8 to the Upper Bala. The Middle 

 Bala of the Cambridge Catalogue receives the fine assemblage of 

 fossils collected from the Bala limestone, sandstones, and slates of 

 North Wales, the Caradoc sandstones and the Horderly limestones 

 of Shropshire, or the true Caradoc. It includes also the fossils of 

 the Coniston Limestone, the Kildare, Craig-Head, and Peebles Lime- 

 stones. The Hirnant Limestone is not included in Sedgwick's 

 Middle Bala, but constitutes the base of his Upper Bala group. The 

 212 species largely illustrate the characteristic fauna of the Caradoc, 

 and the group clearly shows the value of the division (especially 

 with the elimination of the Llandeilo forms) and its separation 

 from the Lower Llandovery (the Upper Bala of Sedgwick), into 

 which only 33 of the 212 species passed. These proportions in the 

 Cambridge collection (as catalogued)^ showing the community of 

 forms between the 3 divisions, show how well the collection was 



