72 DE. WALLICH ON THE THTSICAL 



perfectly preserved state of many of the Cretaceous fossils, are to be 

 discerned the successive stages of a metamorphic action, vs^hereby 

 the protoplasmic matter and silica present on the sea-bed, after 

 having first passed through an organic phase capable of resisting 

 disintegration 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 re- 

 mained incomplete but for the manifest connexion which I was 

 fortunately enabled, in 1860, to trace out between each of the suc- 

 cessive stages referred to and a condition of things 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 Sponges) 

 gradually overwhelms and crushes out the other over indefinite local 

 areas, the strata of chalk in the one case, and the intercalated 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 Atlantic mud ? The answer is, 

 because our specimens of the mud represent only the constituent 

 materials forthcoming at a depth of a few inches beneath the surface, 

 where, if my hypothesis 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 analysis in the 

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



Unfortunately, in such an inquiry, we have to deal with phe- 

 nomena that, owing to the very nature of the conditions, must for 

 ever present many conjectural points too important to be neglected, 

 and yet too obscured in the Cimmerian darkness of the ocean to 

 admit of experimental investigation under identical circumstances in 

 the laboratory. Hence we are driven to fall back on hypothesis, in 

 the hope of a time arriving when, by its means and improved appli- 

 ances, we shall be gradually guided to the truth. 



I will now state, in the form of three hypothetical propositions, 

 the grounds upon which I have been led to infer that the chalk and 

 calcareous mud t were formed under, at least, approximately identical 

 conditions, and am still inclined to regard these two formations as 

 not lithologically distinct. 



1. Were it possible to compare a given quantity of chalk, in the 

 condition in which it was formed at the bottom of the Cretaceous 

 ocean, with a like quantity of recent calcareous mud, no such dif- 



* Much valuable information ** On Quartz and other Forms of Silica " will 

 be found in a paper, bearing this title, from, the pen of Prof. Eupert Jones, 

 F.R.S. Unfortunately I was unable to avail myself of it, being unaware of its 

 existence until the present communication had been laid before the Geological 

 Society. 



t The term " calcareous mud" applies throughout this paper to the common 

 Globigerine ooze as met with in the Atlantic. 



