ANNIVERSARY ADDRESS OF THE PRESIDENT. 



127 



Sandstone." The term Llandeilo was not admitted by Sedgwick 

 either in the ' Synopsis ' or the Woodwardian Catalogue ; therefore 

 great difficulty was and is still felt as to the identification of species 

 long ago collected in certain localities, especially those having 

 reference to the Lower " Llandeilo of Murchison " and the Arenig 

 of Sedgwick ; the faunas of all three groups require careful revision, 

 in consequence of old or early errors, which of necessity demand it. 



Sir Roderick Murchison, in 1833, first noticed the " Caradoc 

 Sandstone "*; in 1834 the same rocks were described by him under 

 the name of the " Horderley and May-Hill Sandstone." In the 

 ' Silurian System,' subsequently published, these strata were called 

 " Caradoc Sandstone," the name being based upon their being highly 

 developed in the neighbourhood of Caer Caradoc. 



In the early history of the Caradoc rocks the fossils of the 

 Pentameras-beds were included in its lists. The Survey subsequently 

 corrected this, by separating the upper part or highest beds of the 

 Caradoc. In 1852 Prof. Sedgwick and Mr. Salter in part corrected 

 this error, and showed that the fossils of the May-Hill group were 

 very distinct from those of the Caradoc Sandstone. Again, the 

 upper Pentamerus-heds rest unconformably on the true Caradoc 

 Sandstone, and the whole pass under the Wenlock Shale. In 

 Shropshire and at Builth the unconformity is visible ; and in the * 

 Malvern area, west of the Herefordshire and Worcestershire Beacons, 

 the Upper Llandovery beds lie directly upon the Upper Lingula-flags 

 or "Dilemma-shales." Again, the Upper Llandovery beds on the 

 banks of the Onny river lie on the upper part of the Caradoc 

 or Bala beds. "West of Wenlock Edge they cover the nearly vertical 

 edge of the Cambrian or Longmynd rocks. " Probably," says Prof. 

 Ramsay, " there is no unconformity so complete yet observed in 

 other members of the British Silurian strata." Besides the researches 

 and large collections of fossils made by the Survey from these 

 rocks, the labours of Sedgwick are preeminently associated with the 

 Caradoc and Bala beds of Wales, through the great memoir on the 

 British Palaeozoic Possils, in which he was so well aided by Prof. 

 M'Coy, and the "Woodwardian Catalogue "t prepared by Salter 

 from the great store of materials in the Woodwardian Museum at 

 Cambridge, and which, many years previously, he had helped 

 Sedgwick to collect, and name, from the classical localities in Wales. 

 To Prof. Ramsay, for his valuable memoir on the Geology of 

 Forth Wales 5, every student is deeply indebted. In this great 

 treatise every detail relative to the physical history and distribu- 

 tion of the Caradoc and Bala rocks and fossils is treated upon ; 

 and to the appendix, originally compiled by Mr. Salter, I have 

 greatly added, especially in that portion treating of the distribution 

 of life, not only for the Caradoc, but through the whole of the for- 



* Proceedings of the Geological Society, 1833, vol. i. p. 476. 



t ' A Catalogue of the Collection of Cambrian and Silurian Fossils contained 

 in the Geological Museum of the University of Cambridge.' By J. W. Salter, 

 F.G.S. With a Preface by the Rev. A. Sedgwick, LL.D.^F.R.S. 



\ Mem. Geol. Surv. of Great Britain, vol. iii. Geology of North Wales. 



