
to the same scales as the soluble silica. 1 In what follows numerical **data** relating to the Chalk, unless otherwise stated, have been obtained from A. J. Jukes-Browne, Cretaceous Rocks of Britain, Mem. Geol. Surv. ; and from the papers on the White Chalk of the Knglish Coast in the Proc. Geol. Assoc. (1899-1903), by A. B. Rowe and CD. Sherborn.2 B. Moore, Trans. Geol. Physics Soc, 1917, p. 1. 
3 W. J. Sollas, The Age of the Earth, London, 1905, pp. 132-65. 
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