murchison on the silurian rocks of n. wales, etc. 165 



January 6, 1847. 



Charles Fraser, Esq. was elected a Fellow of the Society : — 



The following communications were read : — 



1. On the Meaning originally attached to the term "Cambrian Sy- 

 stem," and on the evidences since obtained of its being geologically 

 synonymous with the previously established term "Lower Silu- 

 rian." Bv Sir Roderick I. Murchison, G.C.St.S., V.P.G.S., 

 F.R.S. &c. ■' 



[" By such proofs (organic remains) we are enabled to distin- 

 guish 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 Sysf., 

 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 

 belonging to one or other of those natural divisions*. In a word, 

 the Upper and Lower Silurian fossils published by me had been ap- 

 pealed to by him as the types by which he worked out their equiva- 

 lents in the above slaty tracts ; and even in his memoir published 

 in 184^6, he still divided the older palaeozoic rocks of our island into 

 Upper Silurian, Lower Silurian, arid Cambrian f. In the memoir, 

 however, which he read at the last meeting, Professor Sedgwick took 

 a new course, for which I was unprepared by his previous publica- 

 tions J. After indicating the order of the strata in and beneath the 

 Bala limestone, he now puts forth what I can only understand as this 

 general proposition, viz. that although the fossil type of such rocks 

 is essentially what he and others had recognised as " Lower Silu- 

 rian," the term "Cambrian" ought in preference to be applied to 

 them, because a succession of great physical masses exists in North 

 and South Wales which is not developed in the tracts formerly de- 

 scribed in the Silurian region. In this way, the term Lower Silurian 

 would be suppressed, and the Silurian system, deprived of its lower 

 half, would be split up into two systems of fossiliferous strata beneath 



* See Quarterly Journal Geol. Soc, vol. i. p. 1 ; No. 4. p. 442 ; vol. ii. p. 106. 



t Ibid., vol. ii. p. 130. 



X Let no one suppose, that in consequence of the divergence of our present views 

 on a point of geological nomenclature, there has been the slightest cessation of 

 friendly intercourse between us. Professor Sedgwick wrote to me four months 

 indeed before his memoir was read, and candidly explained his opinions. 

 VOL. III. PART i. N 



