2 The Origin of the 



for a conclusion which many have accepted from 

 him, that flints were generally silicified sponges. I 

 confess that my perusal of his papers and inspection 

 of his illustrations did not appear to me to warrant 

 that idea; which, I find, is disclaimed also by a 

 more recent investigator, who, speaking of Dr. 

 Bowerbank's researches and successive papers, says : 

 u A vast number of interesting facts are here re- 

 corded ; the author's generalization, however, that 

 spongeous tissue is always present in flint, and has 

 brought about its precipitation, 1 hough influencing 

 many geologists even at present, has been objected 

 to by others, and is not in accordance with the 

 views of the author of this paper." The paper 

 referred to is a valuable one by Professor T. Rupert 

 Jones, F.R.S. 2 The same learned writer also rejects 

 the idea, favoured by Dr. G. A. Mantell, of the flow 

 of semi-gelatinous siliceous water over the sea bottom. 

 But he has put forth another theory, tbat flint was 

 formed by the very slow substitution of silica for 

 amorphous lime and calcareous mud, atom by atom. 

 In the case of organic forms, of whatever kind, he 

 supposes that the original organized body had 

 decayed and been replaced by lime and calcareous 

 mud ; and that these materials were then gradually 

 displaced by silica, thus effecting a " creeping meta- 

 morpliic change." 



Later still Mr. R. Mortimer, in a careful paper on 

 the Flints of the Chalk of Yorkshire, 3 has in turn 



2 "On Quartz, Chalcedony, Agate, Flint, Chert, Jasper, and 

 other forms of Silica, geologic lly considered." Proceedings of the 

 Geologists' Association, vol. iv., Xo. 7, p. 439. 



3 Proceedings of the Geologists' Association, vol. v., No. 6, 

 p. 344. To this, and to Professor Jones's paper, my attention was 

 specially and kindly called by Mr. S. R. Pattison, F.G.S. 



