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



The various views on this district may now be thus summarized : 

 A. A general unconformity indicates the commencement of 



a new series. — All. 

 Bj. There is no unconformity in this district. — Bamsai/ ; 



at Moel Tryfaen, Bonney, Raisin. 

 Bj. The unconformity is local only. — Geikie, formerly Blahe. 

 B3. The unconformity is general. — Hughes, Micks, Blake; 



formerly Bonney, Baisin. 



Conclusion 1. There is no break in the series here. — Eamsay, 



Geikie, Bonney ^ Raisin ? formerly Blake. 

 Conclusion 2. The great conglomerate forms the base of 



a new system. — Hughes, Hicks, Blake ; formerly Bonney, 



Raisin. 



Cj. The Moel Tryfaen conglomerate is Cambrian, therefore 

 the underlying beds are Pre-Cambrian. — Hughes, Hicks ; 

 formerly Bonney, Raisin. 



Cj. The beds below the Moel Tryfaen conglomerate are 

 Cambrian; therefore there is no evidence of Pre-Cambriau 

 rocks here, and the age of the conglomerate is doubtful. — 

 Blake. 



Professor Bonney and Miss Raisin s general Objections. 



The authors commence by characterizing my conclusions as 

 "a new and revolutionary hypothesis" ; but it will be seen from the 

 foregoing account that the idea of an unconformity is by no means 

 new. The nature of the rocks in the Moel Tryfaen adit can scarcely 

 be called a " hypothesis," and it is this that is revolutionary in its 

 results, the further extension of the unconformity, which no doubt 

 is new, being thus rendered quite natural. My suggestion also of 

 there being more than one felsite, had been anticipated by Professor 

 Bonney in C. 



As a first objection my critics ask: "To what epoch (from the 

 Menevian onwards) do these so-called Post-Llanberis sediments 

 belong, and where in the adjacent districts may we find beds that 

 can be correlated with them ? " " Of this problem," they say, I have 

 not " succeeded in offering a solution." When they wrote this they 

 cannot have considered my words (p. 465) : " It seems to me most 

 probable that they are extensions of the immediately overlying 

 rocks." These overlying rocks (the Bronllwyd Grit and its 

 associates) do not belong to any epoch from the Menevian onwards, 

 but lie below that formation and below all fossiliferous rocks, except 

 the Peni'hyn pale slates with Conocoryphe viola. The authors have 

 totally misunderstood my suggestion ; moreover, that suggestion 

 about the probable age of the conglomerate may be wrong without 

 affecting the question of the unconformity. 



Next they take me to task for saying that we must see whether 

 this unconformity be local or not, for according to them " it can be 

 no local phenomenon." Plainly it is because I take for granted 

 that a " marked physical break " (Bonney) can be no local 



