ANNIVERSARY ADDRESS OF THE PRESIDENT. 



conformably upon the Tremadoc group on the N. and N.E. side of 

 the anticlinal, and they may be continuously traced for many miles. 

 They occur also at Ramsey Island, and are there 4000 feet thick, 

 chiefly deep-sea deposits, and must have been of great duration, as 

 proved by their varied and distinct faunas. 



Dr. Hicks divides the Arenig group, through its zonal contents, 

 into three subgroups, the Lower, Middle, and Upper Arenig. The 

 lower, or black slaty Arenig, strikes E.N.E. and W.S.W., and has 

 a vertical dip. The cliffs at Whitesand Bay and Road-uchaf, in 

 Kamsey Island, yield the chief fossils. Numerous species of Grap- 

 tolites have been obtained from this lower subgroup ; the Trilobites 

 Asaphus Homfrayi, and Ogygia scutatrix, with Conularia Homfrayi 

 and Lingulella Davisii, especially characterize this lower division, and 

 are associated with Phyllograptus stella, Trigonograptus ensiformis, 

 Callograptus radiatus, and Ptilograptus Hicksii. Dr. Hicks enume- 

 rates 25 species from this division, 28 from the middle, and 33 from 

 the upper*. Asaphus Homfrayi, Ogygia scutatrix, and Conularia 

 Homfrayi are Upper-Tremadoc as well as Lower-Arenig forms, and 

 connect the two formations. I am not aware that Lingulella Davisii 

 ever again appears above this horizon in the Cambro-Silurian rocks. 

 The middle slaty and flaggy groups are also best seen at Whitesand 

 Bay. In 1860 Mr. Gribbs, the late fossil-collector for the Survey, 

 obtained a few fossils here. The characteristic Trilobite Trinucleus 

 Gibbsii was first obtained by him at Whitesand Bay, and subsequently 

 in the Skiddaw beds. This locality has furnished Ogygia bullina, 0. 

 peltata, JEglina grandis, Trinucleus Gibbsii, T. Sedgwickii, Ampyx 

 Salteri, Lingula petalon, and Orthoceras sericeum, with 6 genera and 

 11 species of Rhabdophora ; all the above are essentially character- 

 istic of, and confined to the middle subdivision. Of the Graptolites 

 the chief are Tetragraptus crucifer, T. serra, T. Hicksii, T. Halli, 

 Clematograptus implicatus, Callograptus elegans, and C. Salteri. 



Lithologically the Upper Arenigs resemble the Lower, being fine- 

 grained dark shales, 1500 feet thick ; they underlie the true Lower 

 Llandeilo near Abereiddy Bay, and are conspicuous for the new and 

 distinctive fauna and the first appearance of many genera of Trilo- 

 bites, distinctly marking a complete and progressive change from the 

 fauna of the Tremadoc below towards the introduction of succeeding 

 Llandeilo forms. Llanvirn quarry has yielded to Dr. Hicks a rich 

 group of species " distinct from any previously discovered in any 

 part of the Arenig series at St. David's "t. Most of the genera are 

 new ; and several genera which appear for the first time, culminate 

 in the Llandeilo and Caradoc rocks; these are Hlcenus, Illcenopsis, 

 Barrandia, and Phacops, each having a representative species, and 

 Placoparia, this last a genus new to Britain, hitherto only known in 

 France, Bohemia, and Spain. The occurrence here of this genus is 



* These numbers are doubtless in excess ; v 'many forms must give way on 

 critical examination, numerous species being made upon fragments only. 

 Mr. Lapworth has already reduced them considerably. The Arenig of St. 

 David's may yield 25 species ; the whole Arenig probably about 50 species. 



t Dr. Hicks, Quart. Journ. Geol. Soc. vol. xxxi. p. 174. 



