152 Sir Roderick I. Murchison on the 



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 Orthidse 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 dif- 

 ferences of opinion might exist between those authors concerning 

 points of structure, the arrangement of the masses or their geogra- 

 phical 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 as- 

 surances of my contemporaries, including the Surveyors of the Go- 

 vernment, and by personal visits to North Wales, Westmoreland, and 

 Cumberland, I 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 this 

 principle that I then coloured a geological map of England, at the 

 request of the Society for the Diffusion of Useful Knowledge. 



In the mean time, however, though, for the reason before assigned, 

 I had taken little part in the local question of what might be termed 

 Cambrian, as distinguished from Lower Silurian (leaving that point 

 to be finally settled by the Government geological surveyors), I had, 

 by more extensive surveys in other parts of Europe, gathered posi- 

 tive evidences for coming to a definite conclusion respecting the base 

 of the Lower Silurian rocks. Finding that in Russia, the lowest fos- 

 siliferous band was unquestionably my Lower Silurian group* (a view 

 which was unanswerably sustained by the inquiries of my associates 

 De Verneuil and Von Keyserling), I further saw this group in Scan- 

 dinavia (with nothing but fucoids in its lowest beds), resting at once 

 on pre-existing slaty and crystalline rocks. Northern Europe was 

 first distinctly appealed to as exhibiting the base of the series of ani- 

 mal life, and the Lower Silurian was, by observations in Scandina- 

 via, thus shewn to be the protozoic group. Then came the com- 

 parison of the lowest fossiliferous strata of North America, by Ame- 

 rican authors and Mr Lyell, with a Lower Silurian type similarly 

 related to pre-existing rocks ; and, lastly, in the first chapters on the 

 geology of Russia in Europe and the Ural Mountains, the grounds 

 were fully explained (1845) on which the conclusion had been gene- 

 rally arrived at, that the Lower Silurian was the protozoic or oldest 

 type of animal life yet discovered. 



* See aunoungement to the York Meeting of the British Association, 1844. 



