Vol. 60.] ANNIVERSARY ADDRESS. cift 



II. Bearing of the Evidence on the Causes of 

 Emergence and Submergence. 



Let me now endenvour to set forth the conclusions to which 

 the evidence obtainable in the British Isles points, in regard to the 

 causes which, in this region, have determined the emergence and 

 submergence of land. The vertical range of the changes of level 

 to which I have restricted myself in this Address amounts at 

 least to as much as 700 feet, that is some 600 feet below 

 and 100 feet above the surface of the sea. But it will be remem- 

 bered that, if we include all the deposits that contain recent marine 

 shells in situ, the range of movement will be found considerably to 

 exceed 1000 feet. The problem to be solved is whether this wide 

 amplitude of shift in the relative levels of sea and land should be 

 attributed to variations in the height of the surface of the oceanic 

 envelope, or to secular movements of the terrestrial crust. 



Any change of sea-level might be expected to be general and 

 fairly uniform over iong distances. The area of the British Isles is 

 too restricted to permit us to believe that there could ever have 

 been any serious difference in that level between the eastern and 

 western coasts, or between the northern and southern limits of the 

 country. "Whether, therefore, the surface of the sea rose upon the 

 land or sank away from it, we should find the records of these 

 changes to extend over the entire region and to be marked on the 

 whole by a persistent uniformity of level. But an examination of 

 the evidence fails to furnish proofs of any such extension and 

 uniformity. 



In the first place, the raised beaches, although so perfectly 

 developed over nearly the whole of Scotland, disappear towards the 

 north among the Orkney and Shetland Islands where, had they 

 ever existed, they had every chance of being as well preserved as 

 anywhere on the mainland. These islands obviously lay outside of 

 the area affected by the movement that led to the formation of the 

 beaches. But they could not have escaped from the effects of any 

 rise in the level of the sea. Again, it is incredible that if the 

 great 100-foot terrace, so prominent a feature in Scotland, had been 

 formed by an uprise of the surface of the sea, the same terrace 

 should not have been visible in thousands of favourable positions 

 in England, Wales, and Ireland. Its entire absence cannot be 

 accounted for by the presence of former ice-sheets in these regions, 

 or by subsequent denudation. This absence may surely be taken as 

 proof that the terrace never extended over these parts of our islands. 



