Erratic Blocks of Northern Europe. 147 



Each of these periods must have had a considerable dura- 

 tion. We can readily believe that, w^hile an agent is acting 

 so slowly that a glacier might transport, for hundreds of 

 leagues, the stones and gravel taken from the Norwegian 

 mountains, a long time must have been required, whose mi- 

 nimum of years would be thousands, if the movement of gla- 

 ciers, in our day, be regarded as a criterion. 



The second period must have been at least as long, if we 

 consider the time required for the existence, propagation, and 

 death of an entire fauna, whose numerous remains are found 

 upon a land once submerged. 



Finally, the third period comprehends the historical epoch, 

 when the country was inhabited by the foreign race whose 

 remains are discovered in the peat beds. 



It follows, therefore, that the glacier epoch is not merely 

 an accident in the history of our globe, but it embraces a long 

 period, the more important to the geologist, that it is the 

 connecting link between the antediluvial times and the his- 

 torical era. 



On the Meaning originally attached to the term ** Cambrian 

 System," and on the evidence since obtained of its being geo- 

 logically synonymous with the previously established term 

 " Lower Silurian." By Sir Roderick I. Murchison, 

 G.C.St.S., V.P.G.S., F.II.S., &c. 



[" By such proofs (organic remains) we are enabled to distinguish the 

 Silurian deposits from all others previously described, and through every 

 lithological change we can thereby separate the System into Upper and 

 Lower divisions." — Silurian Syst., p. 9.] 



In a communication upon the Silurian rocks of Sweden, published 

 in the preceding number of the Quarterly Journal of the Geological 

 Society, I stated my objections to some opinions of Professor Sedg- 

 wick, contained in the previous volume, which suggested a re-arrange- 

 ment of the recognised divisions of the Upper and Lower rocks of 

 the Silurian system. I was then chiefly called upon to point out 

 the inapplicability of the proposal to remove the Wenlock formation 

 (or a great part of it) from the Upper to the Lower Silurian ; for 

 even down to last year Professor Sedgwick had invariably spoken of 

 all the lower palaeozoic fossils of North Wales and Cumberland as 



