Flints of the Upper or White Chalk. 199 



death of the sponge that the spicules, ah-eady resting within 

 the protoplasmic mass, combine with it and pass through the 

 phase which has already been described by me in a previous 

 portion of this paper, and was pointed out at p. 72 of my 

 former paper in the extract which will be found ante, p. 192. 

 It only remains for me to mention that the " Coccoliths " which 

 form so prominent a feature in Hackel's figure have, in reality, 

 no connexion whatever with the protoplasmic mass in which 

 they rest. This I maintained in a paper on the nature of the 

 so-called " Bathyhius'' (Ann. & Mag. Nat. Hist., Nov. 1875, 

 p. 325). N6 doubt Coccoliths, subsiding in the shape of 

 disjecta membra of the parent Coccospheres from the surface- 

 waters of the ocean which they inhabit, are constantly 

 showered down in certain regions upon the sponge-fields on 

 the sea-bed below. And when this is the case they no doubt 

 ultimately undergo silicification by replacement, just as the 

 Foraminifera do. But in all probability their extremely 

 minute size and delicate structure, when so silicified, alone 

 prevent us from detecting their spectral pseudomorphs in the 

 flints, except when silicified outside, or, I should rather say, 

 not imbedded directly within the substance, but within a 

 cavity of the siliceous jelly. It is in this wise that they 

 remain perfect in the flint-cavities along with the also free 

 Foraminifera and other included objects. 



Having stated, in a former part of these observations 

 (p. 193), that the strict limitation of all sessile animal life 

 present at the sea-bed to the immediate surface-layer of the 

 muddy deposit, which is an invariable characteristic of the 

 calcareous and probably all abyssal areas where living Protozoa 

 are to be found, supplies the key to the whole of the unique 

 phenomena observable in the flint formation, I will now 

 endeavour to furnish an ideal picture of the condition under 

 which the periodical formation of the strata of flint takes 

 place. The Potstones of the Norwich Chalk appear to me to 

 furnish a supplementary clue to the solution of this problem in 

 spite of the still undetermined question whether they are the 

 fossil remains of some Titanic sponge, like the Ventriculites. 

 Fortunately it is sufficient to know that they were gigantic vitre- 

 ous sponges, and must have grown one after another, each out 

 of the inverted bosom of its immediate predecessor and parent. 

 In this manner, and in this manner only, does it seem possible 

 to explain their forming columnar assemblages, the height of 

 each column, as seen in such faces of the chalk as are exposed 

 to view, approaching 30 feet, each individual in each columnar 

 series being about 3 feet in height. Hence they traverse 

 several successive strata of chalk, passing directly through the 



