Silurian Hocks of North Wales, Sfc, 167 



paratively rare ; but in deciding their age I appealed to the fossils 

 only, and wherever I found certain forms, of Orthidse, Trilobites, 

 Graptolites, &c., I at once mapped in such masses as " Lower Silu- 

 rian." As no one has ever doubted that the name was there rightly 

 applied, I request geologists to read the chapters descriptive of these 

 rocks,* and then to tell me if I have uot in them given a fair illus- 

 tration (though on a smaller scale) of the leading features which are 

 said to characterise the infinitely grander masses of North Wales. 

 With the exception of beds charged with Lingulse and pisolitic iron- 

 ore, and marked by a perfect slaty cleavage, there is, I assert, no 

 essential difference, whether mineral or zoological, between the above 

 tracts of Shropshire and Radnorshire, and the rocks of Caernarvon 

 and Merioneth ; and if the hundreds of feet of the one be expanded 

 into the thousands of feet of the other, and the undulating hills 

 ranging from 1200 to 1800 feet high, be raised into rocky ridges 

 from 2000 to 3000 feet high, geologists will have before them, in 

 my opinion, the Cambrian system as now characterised by Professor 

 Sedorwick. 



Nature's legends are, in a word, found to be composed of the same 

 fossil types in the western parts of Wales, as in the western limits of 

 the Silurian region ; the only difference being, that in the former the 

 spaces between the letters are vastly more expanded, and that the 

 whole region is more slaty, igneous, and crystalline. 



I say it advisedly, and after consultation with good palaeontolo- 

 gists, who have examined the North Welsh fossils, that there is no 

 essential difference between them and those of my Lower Silurian 

 tracts. On the other hand, there are considerable variations in the 

 distribution of the Upper Silurian species of the region I first de- 

 scribed, and those of parts of Wales, Cumberland, and Westmoreland, 

 which have been recognised by geologists, including Professor Sedg- 

 wick himself as Upper Silurian. Why then does he speak of and 

 apply my Upper Silurian types only throughout his last memoir, and 

 not equally depend on those styled Lower Silurian I Why, indeed, is 

 the term •' Lower Silurian" not once employed in his last memoir, 

 though abundantly referred to in all his previous communications, 

 when my types were appealed to? The only answer, it seems to 

 me, which can be given, is, that as the word Cambrian is now de- 

 monstrated to be zoologically synonymous with Lower Silurian, Pro- 

 fessor Sedgwick will not abandon the name he formerly applied to his 

 great physical group, though such name was used before its fossil 

 contents were known. 



The question, then, is simply, Will geologists find it possible to use 

 two terms to designate the very same succession of animal life upon 

 the surrace of the globe \ — such terms being relatively made to de- 



* See Silurian System, chapters xxii. and xxvi. 



