Correspondence — Prof. J. W. Judd. 189 



the present volume (p. 20) are not the same as the Careg Goch 

 grits ; that is to say, I am not speaking of the same localities. 

 Possibly I may have fallen into some error in designating the places. 

 In a thinly populated country, with names, and often a language, 

 that to an English ear are as unintelligible as if they were Pata- 

 gonian, and with a map that (from lapse of time) needs revision, it 

 is difficult to avoid error. I still maintain that the materials of the 

 Anglesey conglomerates are no valid proof in the case of the Twt Hill 

 beds. I never intended to imply that every Cambrian conglomerate 

 must contain felsite pebbles. The language of my article does not 

 warrant the absurd " major premiss " which Dr. Roberts attributes 

 to me. I was obviously speaking (I appeal to any unprejudiced 

 reader to confirm this) of the conglomerates of the Bangor-Carnar- 

 von region, which are full of felsite pebbles, and argued that 

 it was very strange if this one conglomerate of that region, 

 which did not contain felsite pebbles, should be Cambrian — and I 

 pointed out that the absence of these in a distant region could not be 

 adduced in explanation of their absence here. Put concisely this 

 was my argument — " In the Bangor-Carnarvon distinct is a mass 

 of felstone. This has largely supplied materials to the Cambrian 

 and latest Pre-Cambrian conglomerates. In the same district, and 

 near the felstone, are grits and conglomerates in which I do not find 

 felstone fragments. Therefore I think they are not of the same age 

 as the others. As I do not believe thej^ can be later, I suppose 

 they are earlier. The absence of felstone from conglomerates several 

 miles from the mass of this rock does not seem to me to have much 

 bearing on the subject." 



As regards the last paragraph of Dr. Eoberts's article, where he 

 thinks he has made me contradict myself, I beg leave to request him 

 to read my article (pp. 114-117) again, and he will see that I have 

 never admitted the Twt Hill series as Cambrian. He forgets that I 

 maintain that there is a considerable series (larger than that ad- 

 mitted by Prof. Hughes) beneath the Cambrian conglomerate of the 

 Bangor area — Pebidian I suppose we may call it — and I think it 

 more probable that the Twt Hill series belongs to this. The amount 

 of alteration shown by the microscope is considerably greater than is 

 usual in the Cambrian rocks. But really, to criticize fully this 

 last paragraph, I should have to print it with a running commentary, 

 so full is it of assumptions which I should dispute, or inferences 

 which I maintain do not follow from my words. After the above 

 example of his mode of conducting a controversy, Dr. Roberts must 

 excuse me if I take no notice of any further communication which 

 he may make on this subject. T. G. Bonney. 



THE HEADON HILL SECTION. 

 Sir, — As I hope very shortly to have an opportunity of defend- 

 ing the views which I hold (in common with many foreign geologists) 

 concerning the classification of the Isle of Wight Tertiaries, I should 

 not have intervened in the controversy at the present moment, had 

 I not felt myself compelled to protest against certain remarks made 



