§ 13. SILURIAN STRATA OF STAFFORDSHIRE. 769 



logical and zoological characters of this system, and even of . 

 its principal subdivisions, are found to prevail not only in 

 England, and over the continent of Europe, but also in 

 North America, where the Silurian rocks are largely 

 developed, and form the principal ranges of the Alleghany 

 mountains. 



In Cornwall, Silurian rocks appear in several places, 

 emerging from beneath the predominant strata of the dis- 

 trict, the Devonian, and containing characteristic fossils.* 

 But the grand development of this system is in the border 

 counties of England and Wales, including, according to Sir 

 R. Murchison, the whole of the slate rocks of North \Yales ; 

 the fossils found in the latter entirely corresponding with 

 those of the Lower Silurian deposits. " Even in the Lake 

 districts, with a great expansion of equivalents of the 

 Ludlow and \Yenlock rocks, there are no organic remains 

 of higher antiquity than the upper part of the Lower 

 Silurian : and however differing in mineral characters, and 

 containing a few species of fossils hitherto undetermined, 

 all the great inferior masses of that region and of North 

 AVales, are the equivalents of those to which the term Lower 

 Silurian is applied. The Cumbrian system of Professor 

 Sedgwick is, therefore, identified in zoological type with 

 the Lower Silurian deposits/' f 



13. Silurian strata of Staffordshire. — Among the 

 British Silurian districts, the country around Dudley, 

 Walsall, and other parts of Staffordshire, demand especial 

 notice from the interesting circumstances under which these 

 palaeozoic rocks occur ; being isolated, as it were, from the 

 great regions of the formation, and thrown up amidst the 

 newer deposits, like islands in the Triassic and Carbonifer- 

 ous systems : and the- facility of access to these localities, 

 by the railroads from the metropolis, renders them pecu- 

 liarly valuable to the geological student. 



* Sir R. Murchison ; ante, p. 75i- f Ibid, 



