430 Correspondence — Mr. Henry Hicks. 



Mr. Aveline's own evidence also tells completely against himself 

 when he acknowledges that the mudstones are " the equivalents of 

 the Tarannon shales of Wales, and the Coniston grits and flags 

 equivalent to the Denbighshire grits and flags," since recent evidence 

 is entirely opposed to the view, held by the members of the Geolo- 

 gical Survey, and as published in their maps, that the Tarannon 

 shales of Wales overlie the whole of the Llandovery rocks. In a 

 paper which I read at the meeting of the British Association at 

 Bristol last year, I brought forward evidence from numerous sections 

 in North Wales and Shropshire to prove that the pale shales (marked 

 Tarannon Shales on the Survey maps) and some overlying grits in 

 Denbighshire held exactly the same position there stratigraphically 

 as the Llandovery rocks did in South Wales ; and the palseonto- 

 logical facts also were in accordance with this view. Since then 

 further researches have been made, and much additional evidence 

 obtained tending to confirm this view. I have no hesitation now in 

 stating, on the strength of palseontological and stratigraphical evi- 

 dence, that the Tarannon shales are nothing more than equivalents 

 of portions of the Llandovery rocks, chiefly Lower Llandovery, and 

 that the grits associated with and immediately overlying those pale 

 shales in many parts in Denbighshire, and to the east of Corwen, 

 and near Bala, are the equivalents of the Upper Llandovery and 

 May Hill sandstones. Moreover, at these places there is not the 

 slightest sign of an unconformity between the Bala beds and these 

 overlying rocks. I have endeavoured to show in my previous papers 

 that this area, like that of South Wales, probably remained sub- 

 merged during Mid-Silurian changes, and I have only suggested the 

 probability that areas in Cumberland might also have passed through 

 similar changes without having been at the time raised above sea- 

 level. I may be allowed to state, in defence of the value of palseon- 

 tological evidence, that it is seldom found to lead one astray to the 

 extent that lithological evidence seems to have done in the case of 

 these Tarannon shales. It seems indeed strange also that a band of 

 shales avowedly with no fauna at the time should have a distinctive 

 colouring on the Survey map ; when so many truly important series 

 of far greater thickness, and containing numerous rich faunas, should 

 be scarcely recognizable in one tint. 



To Mr. Ward I need only say that the general tone of his letter, 

 to say the least of it, is detrimental to the proper discussion of 

 facts; and that the only argument employed by him, that of 

 authority, is one to which I am not at all prepared to bow. My 

 experience hitherto has taught me to rely rather upon the strength 

 of facts than authority, and to value opinions in proportion as they 

 seem to be supported by the facts. 



Heriot House, Hendon, Henry HiCKS. 



August Sth, 1876. 



