Flints of the Upper or White Chalk. 167 



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 formation of the flints. But the 

 various conditions that present themselves, 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" (see my paper, 

 p. 89). 



It will be seen from this that I had distinctly shown, in 

 the previous part of the paragraph from which the quotation 

 is made, that I laid no claim to originality in reference to the 

 abstract chemical questions concerned on the subject of colloids 

 and notably of silica. Yet, incredible as it may appear, the 

 four next pages of Mr. Sollas's paper, which are taken up 

 with the said " lengthy extract," contain not a single obser- 

 vation that is not wholly connected with the chemical and 

 molecular changes that take place in the formation of flint 

 nodules, and the infiltration with silica of certain shells from 

 the Blackdown Greensand beds, which has no direct bearing 

 whatever on the questions now before us. Indeed the con- 

 cluding paragraph of the extract proves this ; for in it the 

 writer says : — " Thus the crystalline state of flint nodules 

 ofiers us no evidence for or against our theory of the for- 

 mation of these fossils. This theory may be summed up 

 under two heads : — (1) combination of silicic acid with 

 animal matter of various kinds — a chemical fact ; and (2) 

 concentration of the silica from the silicate of animal matter 

 thus formed, hy the extrication of the organic part of the com- 

 pound. This is a pure assumption^ but one which agrees 

 very well with other well-known facts in chemistry " {loc. cit. 

 p. 456). 



Again, speaking of the irregular forms of the flint nodules, 

 Mr. Sollas observes, at p. 459 of his paper : — " These, by 

 their fantastic flowing outlines, are responsible for much of 

 the theorizing which can only regard flint as a silicification of 

 organic matter. Thus, Dr. Wallich repeatedly lays stress on 

 'the unique amoebiform nodulation of the flints,' though one may 

 remark that one of the characteristic features of an amoebiform 

 outline is that it seldom remains the same two minutes to- 

 gether; and this cannot be said of flints, although, as Dr. 

 Wallich speaks in another place of the flints showing ' signs 

 of the specific contractility of colloid silica,' one might infer that 

 he does not regard this character as absent. A flint moving 

 by means of its pseudopodia would be an interesting object ; 

 but perhaps the distinguished writer merely alludes to the 



