BAGSHOT BEDS. 439 



The London Clay is extensively used for making bricks,^ tiles, and pottery. It 

 is also burnt for ballast. The brown colour at and near the surface of the London 

 Clay is merely a colour of decomposition ; the protosalt of iron that gives the 

 bluish tint peroxidating by exposure to atmospheric action.'^ It has been dis- 

 coloured brown to a greater depth, as a rule, than the Kimeridge or Oxford Clays. 

 Chalybeate springs are sometimes met with in the London Clay. Sulphuretted 

 hydrogen is often developed in tunnels and wells excavated in the formation.-* 



The London Clay forms a stiff, tenacious, and sometimes loamy soil, making 

 good pasture-land, and yielding, by the application of marl, good crops of corn. 

 Teazles are cultivated in Essex, and elm, oak, and ash timber in different places. 

 The London Clay is impervious, and yields no water save in the basement beds, 

 or in sandy layers that sometimes occur. 



MIDDLE EOCENE> 

 BAGSHOT BEDS. 



The structure of the Bagshot Beds, so named from Bagshot 

 Heath in Surrey, was first ekicidated by Prof. Prestwich.® The 

 strata are divided as follows : — 



Upper Bagshot Beds. ) t) ^ 



^ ' * I Ti ^ n\ \ Bartonian. 



l\TirMl. Ti.o-=bnt T^.rl= ^arton Clay. S 



IMiddle Baq:shot Beds 1 -r, 11. ti j 

 Bracklesham Beds. 



i Bournemouth Freshwater Beds and 

 Bovey Tracey Beds. 

 Alum Bay Beds. 



The divisions are conformable, and it is often difficult to draw 

 hard lines between them : thus some authorities would link the 

 Barton Clay with the Upper Bagshot Beds, and the Bournemouth 

 Freshwater Beds with the Bracklesham Beds. It seems, however, 

 undesirable to introduce changes that are not absolutely necessary. 

 The Bagshot Beds include freshwater, and marine beds, and they 

 belong to the shallow-water and western equivalents of the great 

 Nummulitic formation.^ 



1 In London, buildings erected from limestone are liable to rapid decay, which 

 arises mainly from the effects of the combustion of coal and the amount of 

 sulphurous acid, and even sulphuric acid, which is brought down from the 

 atmosphere by rain. 



^ Whitaker, Mem. Geol. Surv. iv. 273; see also Parkinson, T. G. S. i. 336. 

 Referring to the odour of clay when a shower of rain first begins to wet a dry 

 clayey soil, Mr. C. Tomlinson has remarked that it is commonly attributed to 

 alumina, and yet pure alumina gives off no odour when breathed on or wetted. 

 The fact is, the peculiar odour referred to belongs only to impure clays, and chiefly 

 to those that contain oxide of iron. — P. Geol. Assoc, i. 242. 



3 Dr. J. Mitchell, Proc. G. S. iii. 151. 



* This division is now termed Upper Eocene, by those geologists who regard the 

 Oligocene as distinct from the Eocene. 



^ Q. J. iii. 378, X. 401. The name Bagshot Heath Sand was given by John 

 Farey, in Sowerliy's Mineral Conchology, vol. i. 1812. See also H. Warburton, 

 T. G. S. (2), i. 48. The beds belong to the ' Lower Marine ' of Webster. 



^ T. R. Jones, P. Geol. Assoc, vi. 437. 



