James Geikle — Denudation in Scotland. 21 



followed by the Glacier ice of that age was influenced to a great 

 degree by the pre-existing configuration of the country. In select- 

 ing matter for illustration, he thought it better to confine himself to 

 one small corner in this great field of inquiry, in the belief that by 

 thus restricting the sphere of their investigations, they should be 

 enabled to attain a better idea of the scope and bearing of the 

 general question. The subject proposed to be considered was denu- 

 dation in Scotland since Glacial times. Now it was very evident 

 that before we could have any proper notion of the denudation of a 

 country, we should first ascertain, as well as we could, the nature 

 and geological origin of the rocks which appeared to have been 

 denuded. For it was plain that until we knew how these rocks 

 came to be amassed, we could never hope to gain any proper estimate 

 of the degree of erosion to which they might have been subjected 

 since the time of their formation. How could we expect to appre- 

 ciate the amount of waste which strata had experienced, until we 

 had first carefully examined these, and considered their geological 

 relations, and gathered together all the evidence we could with 

 regard to their former extension? Denudation was thus a much 

 more complicated study than it might at first appear to be ; and he 

 would repeat that it could only be thoroughly grasped by those who 

 were content to work the matter out for themselves in the field. 

 No doubt we might make up our minds on book evidence as to the 

 probability of this or that theory of denudation ; but it was one 

 thing to believe — it was a very different thing to feel that we believe. 



Before we could arrive at any conclusions regarding denudation 

 in Scotland since the Glacial period, the deposits of that age must be 

 critically examined. We must inquire into the mode of their accu- 

 mulation so as to ascertain what degree of waste they had sustained 

 since deposition, and how much of that erosion might be due to the 

 action of the sea during the marine stage of the Glacial epoch — how 

 much to that of the atmospheric forces in subsequent times. In 

 short, our investigation should involve a study of the whole history 

 of the Drift formation. In the remarks that were to follow, how- 

 ever, he did not pretend to offer anything like a digest of that 

 history. On the contrary, he would limit attention to those portions 

 of the evidence that seemed best fitted to recall the general aspect 

 which appeared to have been presented by the drift accumulations 

 during the various stages of the Glacial period. 



The lecturer then described some of the more characteristic features 

 of these deposits of clay and sand and gravel which are so abundantly 

 scattered athwart the face of the country, and to which geologists 

 had given the general title of the "■ Glacial or Drift Formation." 

 These accumulations were found capable of being divided into more 

 or less well-defined groups, relatively of different ages, but all be- 

 longing to one great geological period. At the base we had the stony 

 ''Till," or Boulder-clay, and above that, in certain cases, came vast 

 heaps of sand and gravel ; while in other districts the Till was over- 



