Ch. XL] 



MASSES OF CHALK IN DRIFT. 



135 



Fig. 122. 



Included pinnacle of chalk at Old Hythe point, west of Sherringham. 

 d. Chalk with regular layers of chalk flints. 



c. Layer called '• the pan," of loose chalk, flints, and marine shells of recent 

 species, cemented by oxide of iron. 



we conceive the till and its boulders to Lave been drifted to tbeir present 

 place by ice, tbe lateral pressure may bave been supplied by the strand- 

 ing of ice-islands. We learn from tbe observations of Messrs. Dease and 

 Simpson in tbe polar regions, that such islands, when 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 sub- 

 merged 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 fallen from cliffs, may 

 have become interstratified. Ice-islands so constituted often capsize when 

 afloat, and gravel once horizontal may have assumed, before the associa- 

 ted ice was melted, an inclined or vertical position. The packing of ice 

 forced up on a coast may lead to similar derangement in a frozen con- 

 glomerate of sand or shingle, and, as Mr. Trimmer has suggested,* alter- 

 nate layers of earthy matter may have sunk down slowly during the lique- 

 faction of the intercalated ice, so as to assume the most fantastic and 

 anomalous positions, while the strata below, and those afterwards thrown 

 down above, may be perfectly horizontal. 



There is, however, still another mode in which some of these bendings 

 may have been produced. When a railway embankment is thrown 

 across a marsh or across the bed of a drained lake, we frequently find 

 that the foundation, consisting of peat and shell-marl, or of quicksand 

 and mud, gives way, and sinks as fast as the embankment is raised at the 

 top. At the same time, there is often seen at the distance of many yards, 

 in some neighboring part of the morass, a squeezing up of pliant strata, 

 the amount of upheaval depending on the volume and weight of mate- 



* Quart. Journ. Geol. Soc. vol. vii. p. 22. 



