Silurian Discussion. 105 



my poetical friend, I advise him to read my last geological paper, 

 should it be printed, not by the glare of his own fireworks, but in 

 the light of day ; and then, should he think a single paragraph of 

 it worth discussing, to discuss it with me in plain prose. 



Before I notice one or two statements of my friend, which are 

 undoubtedly erroneous, let me, shortly as I can, call the attention 

 of the reader to some preliminary facts and principles which vir- 

 tually settle the whole question in debate. 



We began our labours independently in the summer of 1831. 

 In July 1832, I exhibited before the British Association a section 

 through the undulating system of Carnarvonshire, with the excep- 

 tion of a single doubtful group near the Menai. I then determined 

 the true succession of the several subordinate groups of my section 

 and I have never changed it since. During the same summer 

 (1832) I completed one or two parallel sections, from the Menai 

 to the edge of Shropshire, which determined, I believe, correctly 

 the general relations of the whole Cambrian series of Carnarvon- 

 shire, Merionethshire, and Denbighshire. In the autumn of the 

 same year I made two or three rapid traverses through South 

 Wales, which, however imperfect as to details, enabled me to de- 

 termine with absolute certainty that all, or nearly all, the eastern 

 portions of the great undulating system of South Wales (lying to 

 the east of Cardigan Bay) was superior to to the Bala limestone. 



In 1833, my friend exhibited before the British association some 

 of his best sections through a district two years afterwards called 

 Silurian. I followed him with an explanation of my sections, 

 above noticed, across the great series of North Wales. What was 

 then the state of our knowledge, and how far were we agreed \ 

 At that time the overlying flagstones in the north of Denbighshire 

 offered no difficulty. They were the undoubted equivalents of the 

 overlying flagstones near Welsh Pool, afterwards called Upper 

 Silurian. Neither at that time did the coarse sandstones and 

 conglomerates at the base of the Denbigh flags offer any difficulty 

 of interpretation. They appeared to represent, very naturally, the 

 shelly sandstones, &c. (afterwards called Caradoc), of the sections 

 exhibited by my friend. But there was a difficulty in the inter- 

 pretation of my groups on the east side of the Berwyns. Left to 

 my own sections I should, without hesitation, have placed these 

 groups nearly on the parallel of the calcareous slates east of Bala, 

 and called them a part of my Upper Cambrian series ; but this 

 conclusion seemed to clash with my friend's interpretation of the 

 plan of some shelly sandstones (Caradoc) near Welsh Pool. 

 Hence I concluded by asserting " that there must be an overlap of 

 our sections on the east sides of the Berwyns, which could only 

 be explained by a joint interpretation made by us in the field." 



I have noticed the previous facts in historical order, mainly for 



