' HISTOEY OF THE CRETACEOUS FLD^TS. 89 



was known long before deep-sea exploration was dreamt of, is a 

 well-known historical fact ; it has been alluded to by most of the 

 writers who have attempted an explanation of the mode of forma- 

 tion of the flints. But the various conditions that present them- 

 selves, from the earliest elimination of the silica from the sea-water 

 to the period when it becomes finally consolidated, have never, that 

 I am aware, been consecutively followed out. 



There is one distinguished authority, long since deceased, whose 

 unpretentious little volume, ' Eesearches in Theoretical Geology,' is 

 so pregnant with valuable suggestions, which clearly pointed to truths 

 then only looming in the far future of his cherished science, that no 

 apology, I am sure, is needed for offering a short extract from his 

 remarks on the present subject. I allude, of course, to Sir Henry De 

 La Beche. To him, or rather through him in this particular instance, 

 are we indebted for the first clear suggestion in reference to the 

 peculiar molecular behaviour of comminuted particles of silica when 

 kept for a time in suspension along with clayey matter in water. 

 He stated that, according to Mr. Babbage, the mode of formation of 

 the chalk flints received an illustration in the common process of pre- 

 paring the plastic substance for the potteries : when flints, having been 

 previously burnt and ground, were suspended with clayey matter in 

 water, a deposit was produced which possessed the requisite distri- 

 bution of the particles of silica among the clay for pottery purposes ; 

 if this compound were used in proper time, the siliceous particles 

 remained disseminated ; but if allowed to continue too longat rest, 

 the silica became aggregated into small lumps, and the mass was 

 rendered useless for the manufacturer *. 



But that the colloidal idiosyncrasy of silica performed a much 

 more important function in the phenomena connected with the 

 flints than has heretofore been supposed,, appears to me to be indi- 

 cated by the evidence cf the almost perfect incorporation of the 

 organic silica with a colloid material, the unique Amoebiform nodu- 

 lation of the flints, and its homogeneousness, whether occurring in 

 nodules, in continuous sheets parallel to the stratification, or as 

 sluggish overflows into fissures in the Chalk. But for a very 

 highly developed colloidal condition of the materials these peculiari- 

 ties could not, I conceive, have presented themselves so uniformly 

 throughout the formation. Prom a mere aqueous solution the 

 deposit of silica would have exhibited totally different characters ; 

 there would have been a general infiltration into the substance of 

 the chalk, the particles of which would thereby have been cemented 

 together, so as to form a siliceous limestone ; the various minute 

 organic forms in which the silica showed itself, though, no doubt, 

 capable of solution to a limited extent in water charged more or less 

 highly with carbonic acid, and aided perhaps by the stupendous 

 pressure, would have occasionally left more pronounced traces of 

 their original structure than is observable in the body of the flints ; 

 probably all the fossils would have been either infiltrated with silica, 

 or a substitution of that substance would have taken place even more 

 * Published in 1834, pp. 98, 99. 



