APPENDIX. 567 



tending to prove the improbability of the boulder-clays of Northern Ger- 

 many, etc., having been accumulated and distributed underneath a mer 

 de glace. To me they appear to tell a very different tale, and are just 

 such as one might have expected to meet with. In spite of these excep- 

 tions, which are comparatively rare, the distribution of the great mass of 

 stones in the boulder-clays that occur towards the southern margin of the 

 Northern Drift indicates that during the climax of the Ice Age, when the 

 mer de glace attained its greatest development, it flowed in the general 

 directions shown upon the map. The boulder-clays of Northern Germany, 

 etc., like those of other countries, are composed in large measure of the 

 debris of local rocks. They always, in short, reflect the character of the 

 strata upon which, or to the immediate south of which, they he. More- 

 over, commingled with debris of such local origin, fragments derived from 

 greater distances to the north are invariably present, in less or greater 

 abundance. In a word, the phenomena of the German boulder-clays are 

 the exact counterpart of the appearances presented by the boulder-clays 

 of Northern Italy, Switzerland, Scandinavia, Finland, and the British 

 Islands. 



For the termination of the ice-sheet west of the British Islands I have 

 taken the line of 100 fathoms, as indicated upon the Admiralty's charts, 

 but I have followed my friend Mr. Helland in drawing the line off the west 

 coast of Norway in deeper water. 1 Of course these boundaries are only 

 conjectural. We cannot tell how far the ice-sheet flowed out into the 

 Atlantic, because we do not know whether the land stood then at a lower 

 or higher level than it does now. We may safely say, however, that 

 with the sea at or about its present depth, the Scottish ice, which over- 

 flowed the Outer Hebrides, could hardly have reached beyond the line of 

 100 fathoms. But it may well be that the ice streaming out from Nor- 

 way was massive enough to advance considerably farther into the bed of 

 the Atlantic. 



The direction and extent of the glaciation of the Fseroe Islands were 

 determined by Mr. Helland 2 and myself. 3 The ice which covered those 

 islands formed one compact nappe, which flowed outwards in all direc- 

 tions, and, with the sea at its present depth, must have extended as far 

 from the coast as the 100-fathoms line of soundings. The marks of 

 glacial abrasion were traced up to a height of 1600 feet, and as the fiords 

 are here and there 100 fathoms deep, we must add this to the other 

 measurement to get the maximum thickness of the ice (2200 feet) that 

 flowed out from the islands. 



It is most likely that when the glacial phenomena of Iceland come to 

 be better known, we shall find that this island also has supported an ice- 

 sheet, which would flow outwards upon the bed of the sea in the same 

 manner as the local and independent ice-cap of the Fseroes. I have, how- 

 ever, simply coloured the area of Iceland green, like the local centres of 

 glaciation in Central and Southern Europe. 



1 Zcitschr. der deutsch. geol. Ges., 1879, p. 716. 2 Op. et loc. cit. 



3 Proc. Royal Soc. Edin., 1880, p. 495. 



