FUnts of the Upper or White Chalk. 193 



" It is to these questions that I hope, on the present occa- 

 sion, to be able to furnish such answers as sliall, at all events, 

 form the groundwork of a good working hypothesis, and one 

 capable of further elaboration as time and opportunity permit. 

 Meanwliile I may be allowed to state that the conclusions 

 arrived at by me have their origin in the assumption that, in 

 the nearly total elimination of the organic silica from the 

 organic carbonate of lime, in the almost constant aggregation 

 of the colloid silica around some foreign body, in the ultimate 

 consolidation of the colloid material into nodular masses or 

 more or less continuous sheets, in the stratification of these 

 masses and sheets, and, collaterally, in the perfectly preserved 

 state of many of tlie Cretaceous fossils, are to be discerned the 

 successive stages of a metamorphic action, whereby the pro- 

 toplasmic matter and silica present on the sea-bed, after having 

 first passed through an organic phase capable of resisting dis- 

 integration and decay, became once more amenable to those 

 purely material forces in obedience to which they entered upon 

 their new and secondary phase as Flints *. 



" But even yet the chain of metamorphic action must have 

 remained incomplete but for the manifest connexion which I 

 was fortunately enabled, in 1860, to trace out between eacii 

 of the successive stages referred to and a condition of things 

 at the sea-bed then for the first time noticed — namely, that the 

 entire mass of animal life there present is confined to the 

 immediate surface-layer of the muddy deposit, alternating 

 periods being thereby established, during which one of the 

 two predominant animal types (Foraminifera and tSponges) 

 gradually overwhelms and crushes out the other over indefinite 

 local areas, the strata of chalk in the one case, and the inter- 

 calated flint-beds in the other, being the issue of these contests. 



" Should it be asked. Why, then, do we find so striking a 

 lithological difference between the Chalk and the AtUmtic 

 mud ? the answer is, because our specimens of the mud repre- 

 sent only the constituent materials forthcoming at a depth of 

 a few inches beneath the surface, where, if my hypotliesis be 

 correct, there must needs be accumulated nearly the whole of 

 the silica. Whereas, were it possible to obtain specimens, 

 say, from a depth of even a few feet, we should find that all, 

 save the small residuary portion detected by aruxlysis in the 

 Chalk, had in like manner been eliminated from the mud." 



* " Miicli valuable information ' on Quartz and other Forms of Silica ' 

 will be found in a paper bearing this title, from the pen of Prof. Itupert 

 Jones, P\R.S. Unfortunately 1 was unable to avail myself of it, being- 

 unaware of its existence until the present communication had been laid 

 before the Geological Society." 



