176 Rev. J. F. Blake — The Llanheris Unconformity . 



breaking up of the circumjacent deposits during a volcanic eruption, 

 but this explanation is untenable because, as pointed out by Dr. 

 Hicks, the pebbles are of rocks already cleaved. The conglomerate 

 runs in a long line, and its pebbles change character with the rock 

 near which it lies. Near the felsite it becomes most felsitic. On 

 Y Bigl and further north, as also at Moel Tryfaen and Mynydd-y- 

 celgwyn, where it lies nearest purple slate, the fragments like that 

 rock are most abundant, and where at Moel Tryfaen it approaches 

 nearest the upper side of these slates, it contains strange, un- 

 recognizable fragments. In this it shows the character of a shore 

 deposit. 



Although the general objections of my critics are thus disposed 

 of, I do not in the least demur to their conclusion, that " the detailed 

 evidence ought to be of the strongest and clearest nature if it is to 

 establish the supposed unconformity." That is just what it is. ' 



The. Moel Tryfaen District. 



This is the district in which Professor Bonney (C) argued that 

 there was a marked physical break, and Miss Raisin (F) that we see 

 here the base of a series. But now that I give definite proofs of 

 the unconformity they cannot believe it. 



Dealing with the summit conglomerate and the small amount of 

 any conglomerate in the adit section, these authors say " there seems 

 on our theory no other explanation possible than that this con- 

 glomerate is faulted out, and the broad outcrop at the summit 

 might be partly due to such disturbance." We are not told, 

 however, what " our theory " is, nor where the conglomerate is 

 faulted out from, nor how much of the broad outcrop " might be " 

 due to such disturbance. This "explanation" is put forward 

 without any detail that should give us the slightest clue to its 

 meaning, and if we try to guess we are confronted with the puzzling 

 remark, " this seems suggested by the changed dip in the associated 

 green grits on the summit." What the dip was previously and 

 how determined we are not told, so I think it useless to speculate 

 on their meaning. 



The authors disagree with me when T say that there is no green 

 grit on the summit. I will only remark that the green grit seen 

 by them is not the green grit which 1 referred to, which was one 

 occurring between the conglomerate and the purple slates, while, so 

 far as I can judge by the dip given, their "green grit" is part of 

 a small band of false-bedded grit associated with a difi"erent kind of 

 conglomerate of white weathering pebbles, near the opposite side 

 of the outcrop. Here one block shows the dip they state, N.N.W., 

 while an adjacent block shows the opposite, S.S.B. 



Eeferring to my description of the wide spread of conglomerates 

 and grits on the north side of the hill and their generally horizontal 

 trend in an east-and-west direction, the authors differ from me 

 again, at least by implication. I stated that there was a line of 

 crags showing a dip of not more than 5° to the east, and also in 

 a lower part a lenticle of fine grit running almost horizontally 



:fl^ 



