550 PLEISTOCENE AND RECENT. 



out by Mr. Whitaker,i it is in great part due to the dissolution of the Chalk by 

 water hokling carbonic acid, whereby the flints and earthy matter were left ; it is 

 also in part due to relics of Tertiary or Post-Tertiary clays. On the surface the 

 flints are much broken up by natural agencies and by the plough, and sometimes, 

 as near High Wycombe in Buckinghamshire, the fields exhibit a soil of little else 

 than broken flints ; and one would fancy that hardly anything could grow in such 

 places ; but good crops of turnips and mangels are obtained. Even where the 

 flints are picked off, they soon 'grow ' again, if, indeed, any appreciable difference 

 is made. 



Sometimes the Clay-with-flints stretches over the margin of the Upper Chalk 

 resting on the Lower division. In such cases we may look upon it as a residuum of 

 the Upper Chalk which formerly existed there. On the Chalk range of Purbeck 

 we find occasional accumulations of flints ; but the clayey matrix, if it ever occurred 

 there, would soon be washed away, owing to the steepness of the slopes. (See 



Fig- 54. P- 347-) 



The Clay-with-flints lies very irregularly on the Chalk, filling 'pipes,' so that 

 sometimes bare Chalk appears in one place, whilst a clayey deposit twenty or 

 thirty feet in thickness may occur close at hand. It is also noteworthy how trifling 

 a depth of soil serves to hide the Chalk in a field when hard by a pit shows scarcely 

 a trace of any superficial covering on the rock. This is noticeable on parts of 

 Salisbury Plain. Where the pipes penetrate obliquely into the Chalk, the section 

 in the face of a cliff or C|uarry sometimes shows merely a circular pocket some way 

 below the surface. (See pp. 422, 493.) 



While conspicuous in the South of England, over portions of Hampshire, Surrey, 

 Kent, Berkshire, Buckinghamshire, and Hertfordshire, the Clay-with-flints is but 

 little developed in Yorkshire, Lincolnshire, Suffolk or Norfolk. As Mr. S. V. 

 "Wood, jun., remarked, it appears to cover those tracts of Chalk land which were 

 not affected by great submergence daring the Glacial period, and which were not 

 occupied by Land-ice.'- 



MARINE DEPOSITS. 



The Pleistocene and Recent ]\Iarine Deposits include the modern 

 accumulations of sand and shingle along our coasts, certain inland 

 deposits of a similar nature that contain marine shells of existing 

 species, and Raised Sea-beaches. The distribution of sediment 

 beneath the sea does not come within the province of this work, 

 although the subject is of the highest interest to geologists.'* 



These deposits sometimes contain Mammalian remains, as at Silloth Dock, 

 where Bos prifnigemus was found. Here and there considerable accumulations 

 of recent marine shells occur, as at Shellness, by the River Stour, north of Sand- 

 wich, and at Shellness in Sheppey. The beds are worked for making paths. 



Teignmouth,^ Weymouth, and Yarmouth are partly built on recent Marine 

 accumulations. The bank on which the last-named town was built did not 

 become habitable until after a.d. iooo. 



Calcareous sands are sometimes compacted by rain. Prof. A. H. Church has 

 directed attention to an instance at Bude-Haven, in Cornwall, of the consolidation 



1 Explan. Sheet 7 (Geol. Surv.), p. 64 ; Barrois, Ann. Soc. Geol. du Nord, 

 vi. 340. 



* G. Mag. 1S83, p. 340. 



•■^ On this subject see R. A. C. Godwin-Austen, Q. J. vi. 71 ; A. Delesse, 

 Lithologie du Fond des Mers, 1872 ; Lebour, P. Geol. Assoc, iv. 15S. 



* G. W. Ormerod, Q. J. xlii. 98. 



