Vol. 54.] ATfNIVERSAEY ADDRESS OP THE PEESIDEJ^T. Ixxxi 



various points on the hills, in the valleys, and around the coast of 

 North Wales. Wherever the earlier materials have been preserved, 

 especially at high levels, they are seen to consist entirely of local 

 materials, that is, such as would be derived from the immediate 

 neighbourhood, or carried down by streams or ice from the adjoining 

 higher ground. Over this, and partly mixed up with it in the areas 

 not reached by the northern ice, there is an admixture of materials 

 from other Welsh districts ; and in the valleys opening out to the 

 north, and along the coast, there is the further admixture of 

 erratics from northern areas. It is an interesting fact that the 

 boundary-line in the Yale of Clwyd reached by the northern erratics 

 is very little farther inland than the area in which the caverns that 

 we have explored occur. 



Of the history of the subsequent changes I need say but little ; 

 yet it seems to me that there is fairly good evidence to show that a 

 considerable subsidence did take place towards the close of the 

 Glacial period, and that this was afterwards followed by a certain 

 amount of upheaval in the same areas. 



The presence of thick deposits of Drift below the level of the 

 sea, at the entrance to the Yale of Clwyd, with bones of the early 

 Pleistocene mammalia at their very base, is a fairly sure test of a 

 stage of subsidence. Moreover, it is difficult to account for the 

 finding of numerous foraminifera in clays at a height of about 200 

 feet above present sea-level around the coast, ^ unless alternating 

 movements of subsidence and upheaval took place. The marine 

 sand with broken shells at high levels, formerly regarded as sure 

 evidence of subsidence to that depth, must not, I fear, be relied upon 

 too confidently, as in no case has it been clearly shown that the 

 organisms lived in the positions wherein the shells are now found. 

 In some cases, there are also fairly clear indications that deposits 

 have been transported to comparatively high levels by ice which had 

 passed over and scraped up materials from the sea-bottom. 



It seems to me safer, at present, relying upon the evidence which 

 has been brought forward of late years by so many competent 

 observers, to assume that towards the close of the Glacial period 

 the earth-movements produced changes only of a few hundred feet, 

 rather than the great depression and upheaval suggested by the 

 earlier geologists. 



^ See papers by Mr. W. Shone, Quart. Journ. Geol. Soc. vols, yxx (1874) & 

 xxxiv (1878), and by Mr. T. Mellard Reade, ibid. vol. Hii (1897) p. 341. 



