280 Proceedings of the Royal Physical Society. 



ice-sheet, and the origin of the Caithness boulder clay con- 

 taining marine shells. We have recently been furnished with 

 an estimate of the thickness of the ice in Sogne Fiord during 

 the period of extreme cold by Amund Helland. He estimates 

 the minimum thickness at 6000 feet at that particular point, 

 and when we remember that the average depth of the German 

 Ocean is not much more than 240 feet, we can readily under- 

 stand how such a mass of ice could never have floated between 

 Scotland and N'orway. The ice-sheet would move westwards 

 till it found water deep enough to break up the mass, in other 

 words to the lUO fathom line which lies to the west of the 

 Shetland Isles. We conclude, therefore, that during their 

 primary glaciation the Shetland Isles were glaciated by 

 Norwegian ice. 



Further south, in the Mainland, which is by far the largest 

 of the Shetland Isles, all traces of this ancient glaciation have 

 been well nigh effaced by a local ice-sheet, which lingered 

 about the islands long after the Scandinavian glaciers had 

 retreated to their own fastnesses. And this is what might 

 naturally be expected, in spite of the contour of the land, 

 when we consider the high latitude of the islands. Palaeonto- 

 logical evidence assures us that the advent of the ice age was 

 not abrupt, but more or less gradual, and the retreat of the 

 glaciers would be marked by the same gradual change. We 

 may naturally suppose then, that during this recession of the 

 great glaciers, a local sheet clung for centuries to the Main- 

 land accumulating a moraine jprofonde peculiarly its own. 

 Then as the climatic conditions gradually ameliorated, this 

 local sheet eventually gave place to small valley glaciers with 

 their heaps of rubbish and perched blocks. 



III. Notes on Actinia mesembryanthemum, taken from a Bock 

 Pool at North Berivich hy the late Sir John Graham 

 Daly ell in August 1828. By James M'Bain, M.D., 

 R.N. (The living specimen and young were exhibited.) 



The complete life-history of an animal or plant is the 

 ultimate aim and end of biological science. To attain this 

 end, however, in its entirety is, perhaps, impossible ; and it 



