Boulder-Clay. 385 



power of moving ice. Suddenly strip Greenland of its 

 ice-sheet, and it will present a picture, something like 

 the greater part of Britain immediately after the close 

 of this Grlacial period. 



During the time that these results were being pro- 

 duced by glacial action, there were occasional important 

 oscillations in temperature, so that the ice sometimes 

 increased and sometimes diminished, and land animals 

 that lived habitually outside the great glacier limits, at 

 intervals advanced north or retreated south with the 

 retreating or advancing ice. 



Evidence of the same kind is not wanting in 

 England, for erratic stones and large blocks of granite, 

 gneiss, felspathic traps, Carboniferous Limestone, &c. 

 are scattered over the west and east coasts and 

 the central counties of England. Boulders of Shap 

 granite of Cumberland are comfnon in Staffordshire, 

 and even in the valley of the Severn, about twelve miles 

 north of Cheltenham, and they have also been borne 

 across the central watershed of the north into the plains 

 of Yorkshire, near Darlington, and further south on the 

 banks of the Humber. This distribution of erratic 

 stones, on the east of England, throws much light on 

 the subject of the motion of large sheets of glacier-ice, 

 and therefore it is worth while to give a few details, 

 some of which are probably not generally known. 1 



At and a little south of Berwick-upon-Tweed, where 

 the sea-cliffs are clear, or, when the Till has been re 

 moved, the surfaces of quarries of Carboniferous Lime- 

 stone are found to be ice-polished and grooved, the 

 striations point from 10 to 12 south of east, in the 



1 The observations were made in 1863 during an examination of 

 the glacial accumulations on the coast-cliffs by Professor J. Geikie, 

 Mr. Aveline, and myself, and are extracted from my note-book. 



C C 



