220 PROCEEDINGS OE 1HE GEOIOGICAI SOCIETY. [Jan. 22, 



was more than 2000 feet thick when it went to sea. Ice of that 

 thickness would slide along the sea-bottom till it reached water 

 1800 feet deep (300 fathoms). Between Ceantire and F airhead the 

 deepest sounding given is 456 feet ; between May and Instrahull 

 the deepest is only 312 feet.' The limit of 600 feet (100 fathoms) 

 passes far outside the British isles. The limit of 1800 feet is out 

 about Bockall. According to charts, the bottom is chiefly made of 

 sand and shells and mud, the light "drift" which tides pack in 

 harbours. But the lead finds rocky hills and deep hollows under 

 water, and trawlers have fished up great boulders south of Plymouth. 

 Late changes in the level of sea and land are proved by raised 

 sea-margins, by sea-shells far inland, and by submerged peat in the 

 south of Ireland and off "Wales. But if the sea were 1200 feet 

 deeper than it is, glacier ice 2000 feet thick might still slide along 

 the sea-bottom from Scandinavia to Kerry. 



XXI. Landscapes of the glacial period, which I now picture to 

 myself still, are but magnified images of real landscapes. In Green- 

 land and in Spitzbergen, and notably in south-polar regions, very 

 thick broad sheets of ice slide off land into the sea. These crusts do 

 not end suddenly at the water-level ; they break or they slide along 

 the bottom like rafts on slips till they get out of their depth. The 

 ice-rafts meet and join like glaciers on shore in shallow straits about 

 Greenland. Such rafts enlarged would unite if they met in mid 

 ocean. It is well known that glaciers on shore are forced over hills 

 by sufficient pressure from higher hills or from higher snow-heaps. 

 The same glacier partially floated by water can be driven over 

 sunken bills by less force. 



Terrestrial and amphibious glaciers are ice, and have greater mo- 

 bility for weight decreased by partial flotation. Awash in moving 

 water and aground, a glacier pushed seaward is easier to move and 

 is moved by more forces. Ice that slides off Greenland south-east- 

 wards and north-westwards is turned south-westwards by the Arctic 

 current. It would be affected by that current if it were aground all 

 the way to Iceland and Labrador. Were the Arctic current trans- 

 ferred to the. Baltic, and Scandinavian ice enlarged till the whole of 

 that sea was one wet glacier, the laws which govern the circulation 

 of ocean-currents would not be repealed. If the local systems of 

 Greenland, Iceland, and Scandinavia were united in the Atlantic 

 and aground in its shallows, water left fluid in deeps and further 

 south would still move in obedience to existing laws, and would still 

 move ice adrift or awash in it, however large and deep the ice might 

 be. Glaciers did move through hollows which are lake-beds now. 

 I suppose that a far larger glacier than any now extant moved along 

 the beds of shallow seas. In striving to picture the glacial period 

 I invent nothing ; but I strive to shake off ideas of size. The whole 

 world is a very little thing to the solar system ; but so far as we 

 know, the same mechanical laws govern the movements of the whole 

 machine and all its parts. The authors of the ' Reign of Law' and 

 of the ; Theory of Lakes' will agree with this. 



XXII. Ice-marls. — If I reduce a country on the scale of a mile 



