Vol. 60. j ANNIVERSARY ADDRESS. XCi 



Obviously, until accurate information is obtained on all ascertain- 

 able differences of level in the system of our raised beaches, we 

 must remain unprovided with some of the most important material 

 for a discussion of the history of these beaches. It is surely not 

 too much to hope that one or more observers, endowed with the 

 requisite geological knowledge and geodetic skill, may before long 

 be found who will undertake the investigation of this interesting 

 subject, and thus aid in the solution of a problem which does not 

 merely concern the evolution of our own islands, but is of high 

 importance as a question in geological theory. 



The 100-foot terrace carries us back into the Glacial Period. 

 Bones of Arctic species of seals have been obtained from its deposits, 

 and its fine clays and sands point to the settling-down of giacier- 

 mud in sheltered firths. Hero and there, especially where it has 

 accumulated in front of a glacier that bore down coarse detritus, it 

 is marked by a thick terrace of unfossiliferous gravel and sand, as 

 in the remarkable green platforms which form so conspicuous a 

 feature on either side of the narrows of Loch Carron. Its absence 

 from the upper part of this and other sea-lochs has been accounted 

 for, on the supposition that these fjords continued to be filled with 

 ice which barred back the sea and broke off there in icebergs. The 

 deeper-water deposits of the period of this beach are probably 

 represented by the Clyde Beds and their equivalents, with their 

 abundant and well-preserved boreal and Arctic shells. 



The 50-foot beach is much more perfect than the last-named. It 

 must mark a prolonged halt of the land at that particular level. 

 It is in some places a terrace of deposit, in others a platform (or 

 sete) levelled out of the rock. This strand-line also belongs to the 

 Glacial Period. After it was formed, some of the glaciers of Poss- 

 shire and Sutherland came down to the edge of the sea, and shed 

 their moraines upon the terrace. 1 Its organisms are still somewhat 

 Arctic in facies. 



The 25-foot beach is remarkably perfect in some firths, such as 

 those of the Clyde and Forth, as well as along many parts of the 

 eastern and western coasts, and it extends into the North- West of 

 England and the North-East of Ireland. It combines both terraces 

 of deposit with rock-platforms or seter, and its abundant fossils 

 are still common in the neighbouring sea. Though it sometimes 

 presents a striking feature in the topography, it probably marks a 



1 L. W. Hinxman, Trans. Edin. Geol. Soc. vol. vi (1892) p. 249. 



