670 JAMES GEIKIE 



tually become associated with large terminal moraines. In short, 

 the beach in question belongs to that stage of the Ice Age which I 

 have termed the epoch of "District Ice-Sheets and Mountain- Valley 

 Glaciers." During that stage our Highland fiords or sea lochs 

 were invaded by great glaciers, and in their upper reaches we look 

 in vain therefore for any trace of the 100 foot beach. At their lower 

 ends, however, and on the open coast between adjacent sea lochs, 

 the beach is frequently conspicuous. We can thus readily picture 

 to ourselves the general aspect of Scotland at that time. The sea, 

 with its arctic fauna, covered such of our present low grounds as 

 do not exceed 130 feet in height or thereabout. Our estuaries were 

 in winter largely frozen over, while in spring and early summer the 

 ice, broken up into flows, often ran aground in shallow water — con- 

 torting and confusing the marine sediments in course of formation. 

 Many erratics were by the same agency distributed over the floor 

 of the sea. A continuous snow-cap covered the Highlands, from 

 which large glaciers descended in many places to the coast, where 

 they calved their icebergs — another fruitful source of erratics. In 

 the Southern Uplands very considerable ice- streams likewise existed 

 — some of which were of such extent that they escaped from their 

 mountain valleys and deployed upon the low ground beyond, but 

 none reached the seacoast. The central lowlands were at this 

 time clothed with a truly arctic flora — among the characteristic 

 plants being various northern willows {Salix polaris, S. herbacea, 

 S. reticulata), dwarf birch (Betula nana), mountain avens (Dry as 

 octopetala), etc. Associated with these arctic plants in the lacustrine 

 deposits of the time A pus glacialis occurs in great abundance. As 

 this phyllopod is now met with only in fresh-water lakes in Green- 

 land and Spitzbergen, its presence in the ancient aUuvia of central 

 Scotland tells a plain tale. 



All the deposits belonging to this stage, therefore — glacial, fluvio- 

 glacial, lacustrine, and marine alike — we are justified in assigning to 

 the Ice Age, and we may provisionally consider them as representing 

 its closing phase. 



The next succeeding raised beach is met with at a height of 45- 

 50 feet above the present sea-level. Like its predecessor (the 100 

 foot beach), it is best developed in our great estuarine valleys — as 



