86 KEPOHT — 1876. 



jidniit of a doubt that those lakes, ■which are nothing but submerged valleys, are due 

 in part to glacier action, although the other half of the causation on which they 

 depend is to be sought in the subterranean action of subsidence. 



In conclusion, I would observe that although the feet of a great subsidence and a 

 reelevation of the land dmiug the Glacial epoch has been generally admitted to be 

 one of the facts of which there is the clearest evidence, it is nevertheless a fact 

 of which all the conditions and all the consequences have been most imperfectly 

 recognized. 



"S^'ithout venturing to go so far back as to imagine the process of subsidence and 

 submergence, let us only think for a moment of that movement of reelevation 

 which has certainly been one of the very latest of the great movements of geological 

 change. K it took place very gradually or very slowly, it necessitates the supposi- 

 tion that every inch of our mountain-surfaces, up to at least 2000 feet, has been in 

 succession exposed to the conditions of a sea-beach. Yet where are the marks 

 upon them of such conditions ? We may suppose such marks to have been 

 generally obliterated by later subaerial denudation. But against this is to be set 

 the fact that the position and distribution of perched blocks and other erratics 

 deposited by floating ice demonstrate, in my opinion, that very little indeed of 

 such denudation has taken place since they were placed where we now see them. 

 I could take any of you who are interested in this question to a precipitous hill 

 near Inverary, some 1200 feet above the level of the se;i, from the top of which you 

 can look down on the masses of transported rock stranded upon its sides and base, 

 precisely as one might look down from the top of some dangerous reef in the 



E resent ocean upon the debris of a whole navy of ships shattered tipon it in some 

 urricaue of yesterday. There they lie — some more or less scattered, some heaped 

 upon and jammed against each other, with sharp angles and outlines wholly 

 unworn, and, moreover, so distributed that you see at a glance their strict relation to 

 the existing heights and hollows of the laud, which must here have been the shoals 

 and channels of tlie sea. These contours cannot have been materiall}^ changed 

 since that sea was there. It seems that it must have been tliere, geologically speak- 

 ing, only a very few days ago. 



And this conclusion would seem to be confirmed when we observe the phenomena 

 which are present in certain cases where the laud has clearly rested for a consider- 

 able time and the ocean has left in raised beaches the evidence of its work at 

 certain levels. Such raised beaches are to be found at many points all round our 

 western coasts ; but incomparably the finest and most instructive example of 

 them is to be seen on the west coast of the island of Jura, near the mouth of Loch 

 Tarbi.>rt, Jura, and extending for several miles to tlie north. These beaches are 

 visible from a great distance, because then rolled pebbles are composed entirely of 

 the hird white quartzite of the Jura mountains, which resists disintegration and 

 is very imfiivourable to the successful establishment of vegetation. I visited these 

 beaches a few weeks ago, and, measuring the elevation roughly with a graduated 

 aneroid, I found that they represent three more or less distinct stages of subsidence, 

 one beach being about the level of .50 feet above the present sea, another about 75 

 feet, and a third at about 12.5 feet. Some others, which I saw only fi-om a distance, 

 appeared to be higher ; and I believe, but am not quite sure, that further to the 

 north they have been traced to the level of 160 feet. 



But the feature connected with these sea-beaches, and especially with the 

 lowest or the 50-feet beach, is the evidence it affords, first, of the length of 

 time during which the ocean stood at that level, and secondly, and particularly, 

 of the very recent date at which it must have stood there. As regards tlie 

 length of time during which the ocean must ha-^-e stood there, it is sufficient 

 to observe the beautiful smoothness and roundness of the pebbles ; they have been 

 more thoroughly rolled and polished than the corresponding pebbles on the existing 

 shores, equalling in this respect the famous pebble-beds of the Chesil Beach at 

 Portland. Then, as regards the very recent date at whicli the ocean must have 

 stood there, it is difficult to give in words an adequate idea of the impression which 

 must be left on tlie mind of every one who looks at them. You see the curves left 

 by the sweep of the surf, the summit level of its force, aud the hollow behind that 

 summit which is due to the exliausted crest — all as perfect as if it had been the 



