1847.] MURCHISON ON THE SILURIAN ROCKS OF N. WALES, ETC. 169 



geological) line which ran between my working-ground and that of 

 Professor Sedgwicli ; whilst they clearly indicated my belief, that the 

 Silurian system, as distinguished by its fossils, would probably be 

 carried further downwards when the region should have been tho- 

 roughly explored. 



In fact, the problem lo be then solved was — whether the enormous 

 masses of rock which seemed to rise out from beneath the Bala beds 

 would be found to contain a distinct group of organic life? If not, 

 I for one should never have thought of considering them as consti- 

 tuting a system equivalent to the Silurian. '^^'i 



In the meantime other geologists began to occupy themselves iri 

 North and South Wales. Mr. Bowman made an excellent addition 

 to our acquaintance with the former, by showing the exact equiva- 

 lents of some of my Upper Silurian strata in Denbighshire; and whilst 

 Professor Sedgwick w as renewing his labours, Mr. Sharpe also entered 

 the Welsh arena, and contributed, as the Society knows, many new 

 and valuable data. But whoever was the inquirer, no fossils were 

 reported or heard of but " Silurian." In South Wales Sir H. de la 

 Beche and the Government Surveyors showed, that the rocks of 

 certain quartzose and slaty tracts which had been loosely mapped 

 as Cambrian by myself, were, in truth, physically as well as zoolo- 

 gically, the same Lower Silurian strata I had described on their 

 eastern and southern frontier, and that thus, with the exception of 

 certain limited districts occupied by very ancient unconformable 

 greywacke void of fossils, as at St. David's, &c. (like that of the 

 Longmynd in Shropshire, represented in the woodcut p. 167), the 

 lowest fossiliferous strata in South Wales were all conformable and 

 connected masses. Even in a geographical sense therefore, the 

 question whether the so-called Cambrian rocks could be charac- 

 terized by peculiar fossils, seemed to be thus narrowed to the space 

 included between Cader Idris, the Menai Straits and Bala. 



Having satisfied myself in 1842, in company with Count Key- 

 serling, that the prominent fossils in the rocks of Snowdon were 

 nothing but published species of Lower Silurian OrthidaB with 

 simple plaits, I next learnt from Professor Sedgwick himself, that 

 he could discover no types differing from the Lower Silurian in any 

 tracts of North Wales or Cumberland. Referring, indeed, to his 

 works as well as to those of Mr. D. Sharpe, it was evident that 

 whatever differences of opinion might exist between those authors 

 concerning points of structure, the arrangement of the masses or 

 their geographical boundaries, they both agreed as to the persistence 

 of known and published Silurian types through many of the lower 

 slaty strata of North Wales and the Lake Country. Thus fortified by 

 the assurances of my contemporaries, including the Surveyors of the 

 Government, and by personal visits to North Wales, Westmoreland 

 and Cumberland, 1 ventured to comment on the facts in my Address 

 to the Geological Society in 1843, broadly stating, that as the whole 

 of the fossiliferous series of North Wales seemed to exhibit no vestiges 

 of animal life different from those of the Lower Silurian group, the 

 tract must henceforward be considered of that age. It was on 



