668 



GEOLOGY. 



tended beyond the Malvern hills to the banks of the Severn, thus including the north- 

 west of Worcestershire and the southern half of Salop. Here, memorials of the former 

 inhabitants still survive. Siluria is marked in the Ordnance maps as the name of a farm 

 near the centre of the district, not far from the town of New Radnor ; and the Caradoc 

 hills in South Salop commemorate the gallant chieftain who resisted the Roman arms in 

 their neighbourhood. 



It must not be understood that the geological Siluria, as developed on the frontiers of 

 England and Wales, is connected with the limits of the geographical ; but the two are so 

 far coincident as to justify the application of the term to the formations indicated by it. 

 The general form of the Silurian region is that of a crescent, running out from beneath 

 the old red sandstone of Herefordshire, extending northward by Llangollen to the beautiful 

 vale of Clwydd. It is intersected by the Sev.ern at nearly the widest part, which is 

 about twenty-live miles. The river runs obliquely through it from Newtown in Mont- 

 gomeryshire to the plain of Shrewsbury. The southern extremity is a very narrow strip, 

 scarcely four miles across where it is widest, and in some places less than one. it 

 extends from the valley of the Wye at Builth, through the wildest tracks of Brecknockshire, 

 to the vale of the Towy, along which it proceeds to Caermarthen, and thence in a 

 direction nearly west by Haverfordwest to the extremity of Pembrokeshire, terminating 

 at St. Bride's Bay. Besides this continuous tract, there are Silurian outliers obtruded 

 through incumbent groups of strata, through the old red sandstone of Monmouth and 

 Herefordshire, and through the carboniferous series at Dudley and Walsall. 



Since the establishment of the Silurian rocks of South Wales and the border counties 

 as a separate system, it has been discovered, as might have been inferred from analogy, 

 that the same series of strata is very widely distributed, and appears in very distant 

 regions of the globe. Formations belonging to the same class are recognised, and of 

 considerable dimensions, between Kendal in Westmorland, where they repose upon the 

 Cambrian rocks> and Kirkby Lonsdale in Yorkshire, where they dip under the old red 

 sandstone of the valley of the Lune. They occur also obscurely in Devon and Cornwall. 

 In the south of Ireland, on the southern frontier 4 ^ the Ardennes in France, in Servia 

 and the adjacent parts of Turkey in Europe, in the neighbourhood of Smyrna and the 

 Cape of Good Hope, in the Hartz mountains and in Norway, the Silurian system 

 appears. It has been stated by Mr. Conrad, of the New York Geological Survey, that he 

 can not only identify the Silurian system generally with rocks in that state, but also 

 the subdivisions ; and that the strata are more fully developed in that country than in 

 England, particularly about the borders of the great lakes Huron and Superior. From 

 the Falkland Islands, Mr. Darwin brought home masses of rock charged with fossils, 

 very nearly related to, if not identical with, those of our Caradoc sandstones. The disco- 

 very of this wide diffusion of the strata has produced the reflection, that the generic 

 appellation, although perfectly appropriate With reference to British geology, is inadmis- 

 sible beyond this boundary ; that to classify rocks of the same lithological character, 

 occurring in remote situations, under a title belonging to a particular locality, is invidious 

 and incorrect. Hence, a transatlantic Geologist, after stating that particular rocks of his 

 district range with Mr. Murchison's Silurian group, remarks: "We do not, however, 

 see any propriety in applying a local term to a class of rocks abundant in every quarter of 

 the globe ; we have the same right to our Nerepsis, Mispek, and Quaco rocks, as our 

 contemporaries across the Atlantic have to their Ludlow, Wenlock, and Caradoc rocks," 

 subdivisions of the Silurian system. But it may be replied to this somewhat jealous 

 observation, that as Mr. Murchison led the way in demonstrating and describing a com- 

 plete succession of fossiliferous deposits interpolated between the oldest slaty rocks and the 

 Old red sandstones, to him it of course belonged to denominate the series by a collective 



