222 CONTORTED DRIFT. CHAP. XII. 



it into their present position. The level surfoce of the chalk 

 in situ (f/) may be traced for miles along the coast, Avhere it 

 has escaped the violent movements to which the incumbent 

 drift has been exposed.* 



We are called upon, then, to explain how any force can 

 have been exerted against the upper masses, so as to produce 

 movements in which the subjacent strata have not partici- 

 pated. It may be answered that, if we conceive the till and 

 its boulders to have been drifted to their present place by 

 ice, the lateral pressure may have been supplied by the strand- 

 ino- of ice-islands. We learn, from the observations of 



try ' 



Messrs. Dease and Simpson in the polar regions, that such 

 islands, wdien they run aground, push before them large 

 mounds of shingle and sand. It is therefore probable that 

 they often cause great alterations in the arrangement of pliant 

 and incoherent strata forming the upper part of shoals or 

 submerged banks, the inferior portions of the same remaining 

 unmoved. Or many of the complicated curvatures of these 

 layers of loose sand and gravel may have been due to another 

 cause, the melting on the spot of icebergs and coast-ice in 

 which successive deposits of pebbles, sand, ice, snow, and mud, 

 together with huge masses of rock fiillen from chffs, may have 

 become interstratified. Ice-islands so constituted often cap- 

 size when afloat, and gravel once horizontal may have assumed, 

 before the associated ice was melted, an inclined or vertical 

 position. The packing of ice forced up on a coast may lead 

 to a similar derangement in a frozen conglomerate of sand or 

 shingle, and, as Mr. Trimmer has suggested,! alternate layers 

 of earthy matter may have sunk down slowly during the 

 liquefaction of the intercalated ice so as to assume the most 

 fantastic and anomalous positions, while the strata below, 



» For a full account of the drift of f Quarterly Journal, Geological 



East Norfolk, see a paper by the author, Society, vol. vii. pp. 22, 30. 

 Phil. Magazine, No. 104, May, 1S40. 



