vr SedgwicKs Cambrian System 261 



named by Professor Sedgwick the Upper Cambrian." 

 Sedgwick, on the other hand, confessed that neither in the 

 Lake District nor in North Wales was the stratigraphical 

 succession unbroken, and that in these regions it was im- 

 possible to tell " how many terms are wanting to complete 

 the series to the Old Red Sandstone and Carboniferous 

 Limestone." 1 He adopted a threefold subdivision into 

 Lower, Middle, and Upper Cambrian, but this classification 

 rested merely on mineral characters, no attempt having 

 yet been made by Sedgwick to determine how far each of 

 his subdivisions was defined by distinctive fossils. 



Eventually it was ascertained that the organic remains 

 in the upper part of the Cambrian system were the same 

 as those found in the Lower Silurian formations as defined 

 by Murchison. It was obvious that the one series was 

 really the equivalent of the other, and that they ought not 

 to be classed under separate names. The officers of the 

 Geological Survey, working from the clearly defined 

 Silurian formations, could draw no line between these and 

 those of North Wales, which Sedgwick had classed as 

 Cambrian, rinding the same fossils in both, they felt 

 themselves constrained to class them all under the same 

 designation of Silurian. Murchison, of course, had no 

 objection to the indefinite extension of his system. Sedg- 

 wick, however, after some delay, protested against what 

 he considered to be an unjustifiable appropriation of terri- 

 tory which he had himself conquered. And thus arose a 

 misunderstanding between these two old comrades, which 

 deepened ere long into a permanent estrangement. 



It is not my intention to enter here into the details of 



1 Op. cit. 



