ON THE DRIFTS OF THE VALE OF CLWYD. 



73 



7. On the Drifts of the Yale of Clwyd and their Relation to the 

 Caves and Cave-deposits. By T. M c Kenny Hughes, M.A., 

 F.G.S., Woodwardian Professor of Geology, Cambridge. (Read 

 November 17, 1886.) 



[Plate IX.] 

 Part I. 

 Introduction. 



The questions here involved are many and various, and their consider- 

 ation carries us from one place to another over a very wide area. 



We cannot safely draw inferences as to the age and origin of any 

 drifts on the borders of a mountain-land without, on the one hand, 

 tracing it up to the source from which it was transported, to see 

 whether we can explain the distribution of the various kinds of 

 material of which it is composed, and, on the other hand, following 

 it as far as possible down over the lowlands, to see whether any 

 succession of deposits or organic remains or evidence as to its former 

 extent can be made to throw light on the conditions of the age in 

 which it was distributed. 



And, seeing that most caves have been formed and filled during 

 the age of accumulation of the various superficial deposits which 

 we include under the name "drift," we cannot safely speculate 

 upon the age or origin of the one set of phenomena without con- 

 sidering all the evidence to be derived from the other also. 



Only in the hilly districts can we find caves at all, and, generally, 

 the more important occur along the outskirts of the high lands, 

 where drifts of various character are apt to be found. The rela- 

 tion of the local drifts to the caves may be of great interest if the 

 exact place and age of those drifts have first been clearly made out. 



We must first therefore inquire whether it is possible to estab- 

 lish a local succession in the drifts ; whether the classification 

 so suggested fits in with the conclusions arrived at in adjoining 

 districts ; whether we can arrive at any connected history of the 

 sequence of events connected with the caves consistent with all the 

 information so gathered. 



Such are the questions I invite the Society to discuss with 

 reference to a part of North Wales, and I propose to bring forward 

 the evidence I have collected on the subject in the following 

 manner : — 



A. The Drifts of the Vale of Clwyd. 



1. The Arenig Drift. 



2. The St. Asaph Drift. 



3. The Surface-drift. 



B. The Caves of the Vale of Clwyd. 



1. The Caves. 



2. The Cave-deposits. 



