452 Mr. W. J." Sollas on the Flint 



The first explanation may best be stated in Dr. Wallich's 

 own words. Thus, speakingof the irregular nodules, he says: — 

 . . . . " those characteristic amcebiform outlines which, ac- 

 cording to my hypothesis, are dependent on the presence 

 of, and the combination of the silica with, the accumulation of 

 nearly 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 this 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 

 almost as consecutively followed out as in Dr. Wallich's paper 

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

 make no apology for giving here a rather lengthy extract 

 from it. 



It is " necessary to inquire next how far there are any 

 facts in chemistry or physics which throw any light on this 

 singular and intimate connexion between animal matter and 

 mineral substances. One fact noticed by Graham, and which 

 any one may experimentally verify, is very noticeable, viz. 

 that silicic acid has the property of actually combining with 

 such substances as albumen and gelatin to form with them dis- 

 tinct chemical compounds, silicate of albumen and silicate of 

 gelatin. 



" If, then, such animals as sponges flourish in the bed of an 

 ocean which contains a sensible amount of silicic acid, when 

 these creatures die the consequence will be that the water, 

 finding ready access to every corner of their organism, will 

 yield its silicic acid to the greater attraction of the sponge- 

 fibres, and will form with them a well-marked, definite chemi- 

 cal compound ; and it is conceivable that in course of time this 

 compound, like all other highly complex organic bodies, will 

 decompose, its carbon, hydrogen, nitrogen, and oxygen will 

 disappear, and the result will be a concentration of the silica 

 in the form of flint, very much in the same way as carbon 

 concentrates in coal. 



" Other processes, of course, would proceed at the same 

 time, aiding to the same end ; any sodic silicate in the water 

 would probably be decomposed by the carbonic anhydride 

 escaping from the decomposing animal matter, and would form 



