114 The Cambrian and 



Silurian region, and he will see, that if the Lower Silurian rocks, 

 which are represented as ranging through Brecon and Caermar- 

 thenshire by Llandovery and Llandeilo, be converted into Cam- 

 brian, the Silurian System (hitherto the only published type of 

 comparison) will be reduced to an almost imperceptible line. 

 Again, let the inquirer look in the same map at Broad Sound, 

 in Pembrokeshire, where, to my great satisfaction, I first found all 

 the Silurian formations, from the Ludlow to the Llandeilo, rising 

 out from beneath the old red-sandstone, and then tell me if fiat 

 justitia will reconcile geologists to the abstraction of the half of 

 what I have proved to be Silurian, leaving me in a corner of one 

 bay with my Upper Silurian rocks only — the pars pro toto ? This 

 must be the practical British issue of the adoption of the nomen- 

 clature of Professor Sedgwick. 



The geologists and naturalists of the Government Survey, being 

 satisfied that there is but one series of rocks and fossils in the bay 

 of Pembroke above cited, have further proved, by admeasurement, 

 that this same " Silurian System" is spread over nearly all Wales. 

 To those persons aud their works I again refer my friend. Esta- 

 blishing the Silurian System, I applied it to some foreign countries. 

 The Government surveyors have spread it over Cambria, not 

 through any mistake whatever, but on the true principle of assimi- 

 lating things unknown to things which have been described. 



I now terminate on my part a controversy which has given me 

 much pain, yet from which I could not shrink ; for mine is not 

 merely a combat pro aris Silurianis, but the defence of a classifi- 

 cation which I believe to be natural and indestructible. And 

 although my old friend has, both in his first abstract (see Literary 

 Gazette, March 6) and his last letter, used some racy expressions, 

 and that I have thought it right to speak plainly, I look with un- 

 diminished confidence to our sliding down the shady slope of life 

 with that mutual esteem and regard which were formed when 

 climbing many a hill together both at home and abroad. 



In our general geological views we are as united as in days of 

 vore. Roderick Impey Murchison. 



3. — Professor Sedgwick's Reply to the preceding Letter of 

 Sir R. L. Murchison. 



Norwich, May 8. 

 Sir, — My copy of the ' Literary Gazette ' for April 24 having 

 been addressed to me at Norwich, did not reach me until my 

 arrival here the early part of this week ; and now (after having 

 been several days indisposed and quite incapable of writing) I send 

 my final answer to the last Silurian comments of my friend Sir 

 R. I. Murchison. My replies shall be as specific and as short as 



