Flints of the Upper or White Chalk. 165 



other opinion whatever on the veins, for reasons which I con- 

 sidered sufficient — the allusions to sluggish overflows into 

 the fissures of the chalk being made solely with a view 

 to point out that, had they been filled with an aqueous 

 solution, the fissures would not only have been lined with 

 silica, but the walls of the fissure would, to a considerable 

 depth, have become silicified through the absorbent power of 

 the chalk. This view I still regard as valid, and as appli- 

 cable to the tabular layers of chalk also. The following is 

 the sentence from which Mr. Sollas has detached and quoted 

 (as I shall show he has done in other instances) an incom- 

 plete passage, in order that he might impugn it : — " 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 in- 

 dicated by the evidence of the almost perfect incorporation of 

 the organic silica with a colloid material, the unique amoebi- 

 form nodulation of the flints, and its homogeneousness^ whether 

 occurring in nodules, in continuous sheets parallel to the strati- 

 fication, or as sluggish overflows into fissures in the chalk " 

 [loc. cit. p. 89) . 



Again, at p. 451 of his paper Mr. Sollas says : — " In 

 attempting to find an explanation for the form of these flints 

 we may consider the following suppositions : — (i) The form 

 may have been determined by the presence of animal matter 

 (protoplasm, Wallich), or (ii) of the products of its decompo- 

 sition," &c. ..." The first explanation may best be stated in 

 Dr. Wallich^s own words. Thus, speaking of the irregular 

 nodules, he says : — ' those characteristic amosbiform outlines 

 which, according to my hypothesis, are dependent on the 

 presence of, and the combination of the silica with, the accu- 

 mulation of neai-ly pure protoplasm still sufficiently recent to 

 have resisted admixture with calcareous or other matter ' {loc. 

 cit. p. 79). As I have already shown in the earlier part of 

 this paper that flints originate as silicified chalk, we need not 

 spend time on a formal confutation of Dr. WallicK's hypothesis] 

 but when Dr. Wallich remarks that ' 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 ' (loc. cit. p. 89) , I would take the liberty to refer 

 him to a paper of my own, printed in abstract in the Quart. 

 Journ. Geol. Soc. vol. xxix. p. 76 (1873), where the steps are 

 perhaps as consecutively folloiced out as in Dr. Wallich's paper 

 itself. As my paper has never been published in full, I shall 



