No. 3.] HUNT — ON CAMBRIAN AND SILURIAN. 283 



mynd 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 Brecon- 

 shire, and to the west of Llandovery in Caermarthenshire ; con- 

 stituting an underlying 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 fossilifevous formations. 



In the Philosophical Magazine for July, 1835, Murchison 

 gave to the four formations above named the desio-nation 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 in the study of these rocks, 

 Murchison, as he tells us, urged him to give them a British geo- 

 graphical name. Sedgwick accordingly proposed for this great 

 series of Welsh rocks, the appropriate designation of Cambrian, 

 which was at once adopted by Murchison for the strata supposed 

 by him to underlie his Silurian system. [Murchison, Anniv. 

 Address, 1842; Proc. Geol. Soc. III., 641.] This was almost 

 simultaneous with the giving of the name of Silurian, for in 

 August, 1835, Sedgwick and Murchison made communications 

 to the British Association at Dublin on Cambrian and Silurian 

 Rocks. These, in the volume of Proceedings (pp. 59, 60) appear 

 as a joint paper, though from the text they would seem to have 

 been separate. Sedgwick then described the Cambrian rocks of 

 North Wales as including three divisions: 1. The Upper Cam- 

 brian which occupies the greater part of the chain of the Berwyns, 

 where, according to him, it was connected with the Llandeilo 

 formation of the Silurian. To the next lower division, Sedgwick 

 gave the name of Middle Cambrian, making up all the higher 

 mountains of Caernarvon and Merionethshire, and including the 

 roofing-slates and flagstones of this region. This middle group, 

 according to him, afi'orded a few organic remains, as at the top 

 of Snowdon. The inferior division, desiirnated as Lower Cam- 

 brian, included the crystalline rocks of the south-west coast of 

 Caernarvon and a considerable portion of Anglesea, and con- 

 sisted of chloritic and micaceous schists, with slaty quartzites and 



