386 Prof. T. Sterri/ Hunt — On Cambrian and Silurian. 



limestone in the Berwyn hills is overlaid by many thousand feet of 

 strata as we proceed eastward along the line of section, until at 

 length the eastern dip of the strata is exchanged for a westward 

 one, thus giving to the Berwyn chain, like that of Snowdon, a 

 synclinal structure. As a consequence of this, the limestone of 

 Bala re-appears on the eastern side of the Berwyns, underlaid as 

 before by a descending series of slates and porphyries. These 

 results, with sections, were brought before the British Association 

 for the Advancement of Science at its Meeting at Oxford in 1832; 

 but only a brief and imperfect account of the communication of 

 Sedgwick on this occasion appears in the Proceedings of the Associa- 

 tion. He did not at this time give any distinctive name to the series 

 of rocks in question. (L. E. and D. Philos. Mag., 1854:, iv., vol. 

 viii. p. 495.) 



Meanwhile, in the same year, 1831, Murchison began the exami- 

 nation of the rocks on the river Wye, along the southern border of 

 Eadnorshire. In the next four years he extended his researches 

 through this and the adjoining counties of Hereford and Salop, 

 distinguishing in this region four separate geological formations, 

 each characterized by peculiar fossils. These formations were 

 moreover traced by him to the south-westward across the counties 

 of Brecon and Caermarthen ; thus forming a belt of fossiliferous 

 rocks stretching from near Shrewsbury to the mouth of the river 

 Towey, a distance of about 100 miles along the north-west border 

 of the great Old Red Sandstone formation, as it was then called, of 

 the west of England. 



The results of his labours among the rocks of this region for the 

 first three years were set forth by Murchison in two papers pre- 

 sented by him to the Geological Society of London in January, 1834. 

 (Proc. Geol. Soc, vol. ii. p. 11.) The formations were then named 

 as follows in descending order : 1. Ludlow ; 2. Wenlock, consti- 

 tuting together an upper group ; 3. Caradoc ; 4. Llandeilo (or 

 Builth), forming a lower group. The Llandeilo formation, according 

 to him, was underlaid by what he called the Longmynd and Gwas- 

 taden rocks. The non-fossiliferous strata of the Longmynd hills in 

 Shropshire were described as rising up to the east from beneath the 

 Llandeilo rocks ; and as appearing again in South Wales, at the 

 same geological horizon, at Gwastaden in Breconshire, and to the 

 west of Llandovery in Caermarthenshire ; constituting an under- 

 lying series of contorted slaty rocks many thousand feet in thickness, 

 and destitute of organic remains. The position of these rocks in 

 South Wales was, however, to the north-west, while the strata of 

 the Longmynd, as we have seen, appear to the east of the fossiliferous 

 formations. 



In the Philosophical Magazine for July, 1835, Murchison gave to 

 the four formations above named the designation of Silurian, in 

 allusion, as is well known, to the ancient British tribe of the Silures. 

 It now became desirable to find a suitable name for the great inferior 

 series, which, according to Murchison, rose from beneath his lowest 

 Silurian formations to the north-west, and appeared to be widely 

 spread in Wales. Knowing that Sedgwick had long been engaged 



