27 



most characteristically developed. Where the liroestone is impure 

 there the siliceous nodules become cherty, but even where 

 carbonate of lime is absent, as in the sponge-beds of Westphalia, 

 there is a tendency to form nodules. These were at first taken 

 to be gigantic sponges — resembling somewhat the Paramoudras 

 of the Norfolk Chalk — but were afterwards shown by Zittel to be 

 "nodular masses of rock, filled with sponge .^spicules or their 

 casts" (Hinde). 



But in truth the question of the formation of Flints is part 

 and parcel of a still wider question ; one which must take into 

 account such phenomena as the silicification of huge trees — a 

 forest in fact — in the plains of Arizona, the sjlicified wood of the 

 desert near Cairo and of New Zealand. Unfortunately the 

 Chemistry of Geology lags far behind the phenomena for the 

 explanation of which its help is required, and geologists must 

 wait for the help of the sister science before they are able to solve 

 many of the problems which now perplex them. 



WORKS REFERRED TO OR CONSULTED. 



Abbott, G. — Was the Deposit of Flint and Cbalk Contempor- 

 aneous. Geolog. Mag., 1893, p. 275, 477. 



Bowerbank, J. S. — Prcc. Geolog. Soc, vol. iii., p. 271, 431. 



Browne-Jukes, A. J. — ^Relative Age of Flints, Geolog. Mag., 

 1893, p. 315. 



Buckland, Dr. — Geolog. Trans., vol. iv., p. 416. 



Byron, G. A. — Silicification of Oi'ganic Bodies. Prac. Roy. 

 Phys. Soc. of Edin., 1863. 



Challenger Reports, vol. xxi., parts 1 and 2. 



Charlesworth, E. — London Geolog. Journal, 1846. On Paramou- 

 dras. Trans. Vict. Inst., xxvi. 



Dixon and Jones. — Geology of Sussex, pp. 125-448. 



Geikie, Sir A.— Text Book of Geology, 1879, p. 347. 



Graham. — On the Properties of Silicic Acid, &c. Chemical 

 Researches, p. 618. 



Green, Prof. A. H.— Geology. London, 1876, p. 178. 



Hinde, Dr. G. J. — Fossil Sponge Spicules from the Upper 

 Chalk. Munich, 1880. On Beds of Sponge Remains in the 

 Lower and Upper Greensands of the South of England. 

 Transactions <f the Royal Society, 1885. Catalogue of 

 Fossil Sponges in the British Museum, 1883. 



