148 Sir Roderick I. Murchison on the 



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 1846, he still divided the older pala30zoic rocks of our island into 

 Upper Silurian, Lower Silurian, and Cambrian. "j" In the memoir, 

 however, which he read at the last meeting of the Geological Society, 

 Professor Sedgwick took a new course, for which I was unprepared 

 by his previous publications.]: 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 Silurian," the term " Cambrian" ouoht in 

 preference to be applied to them, because a succession of great phy- 

 sical masses exists in North and South Wales, which is not developed 

 in the tracts formerly described in the Silurian region. In this way, 

 the term Lower Silurian would be suppressed, and the Silurian sys- 

 tem, deprived of its lower half would be split up into two systems of 

 fossiliferous strata beneath the Devonian, instead of continuing to be 

 one natural series divided into two groups, as first established in Bri- 

 tain, and subsequently extended to other parts of Europe. 



Painful as it is to me to oppose my distinguished associate, — the 

 friend with whom I have so often co-operated, and to whom I dedi- 

 cated the " Silurian System," I am compelled to resist a proposition, 

 the adoption of which would, I conceive, be productive of great dis- 

 service to the progress of geology ; and he must therefore excuse me 

 if I defend the ground of Caractacus, with a pertinacity approaching 

 to that of the old Silurian chief. 



I shall therefore treat this question under the following heads : — 

 the origin of the terms " Silurian" and " Cambrian" — the nature 

 and progress of the classification to which the term " Silurian" re- 

 ferred, whether in Great Britain or the continent, — and the effects of 

 the adoption of the proposed change upon geological science.' 



After labouring during four years in certain Welsh and English 

 counties, in which I had traced out and defined a succession of fos- 

 siliferous deposits, from the base of the old red sandstone down to 

 certain older rocks then called " slaty greywacke," I was urged by 

 many geologists to designate such rocks by a distinct name. Ac- 

 cordingly in June 1835, J I applied to them the term " Silurian Sys- 



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



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



} 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 ces- 

 sation of friendly intercourse between us. Professor Sedgwick wrote to nie 

 four months indeed before his memoir was read, and candidly explained his 

 opinions. 



+ Phil. Mag., June 1835, vol. vii., p. 50. 



