174 Dr. Wallich on the Origin of the 



that " the once existing spicules are absent from the Trim- 

 mingham deposit — not because they have been washed away, 

 but dissolved ; for they are invariably absent in fossil sponges 

 and stratified deposits. Neither Zittel nor I " (he says) " have 

 seen a trace of them ; and my observations on the compara- 

 tive readiness with which they undergo solution in — CAUSTIC 

 POTASH, serve to explain their absence'''' ! [he. cit. p. 442). 



If tliese are not " inferences," they are something more, 

 namely pure assumptions — the first an improbable assump- 

 tion, the second worse than improbable, since every school- 

 boy knows nowadays what the action of "caustic potash" is 

 on silica, and that caustic potash is certainly not one of the 

 ingredients which chemical analysts have heretofore detected 

 in oceanic waters. It is therefore " a self-evident truth" that 

 the solution of .the Trimmingham sponge-spicules on the sea- 

 bed could not, under any known conditions, have been due to 

 the substance referred to, even were it possible for the alkali 

 to exist in sea-water in the form of hydrate. Besides there 

 is no other substance in sea-water which possesses even an 

 approximate solvent energy upon silica. " The chemical fact" 

 referred to {loc. cit. p. 456) cannot, therefore, under the most 

 strained interpretation, be regarded as " serving to explain," 

 or being connected with, "the absence of the spicules" from 

 the Trimmingham deposit. Nor, coupling it with what has 

 been previously advanced, can it be regarded otherwise than 

 as demolishing Mr. Sollas's claim to having made a demon- 

 strated fact occupy the place cither of analogy or inference. 

 And, going yet a step further, if we take the whole of the facts 

 that have up to this point been recorded, I venture to think it 

 has been indisputably proved that no parallel can be drawn, 

 for the purposes of the present inquiry, between the Trim- 

 mingham chalk with its fiints and the White or Upper Chalk 

 with its flints, or even the typical calcareous deposits of the 

 modern Atlantic sea-bed. Should this conclusion be correct, 

 it follows, as a natural consequence, that the whole of the 

 arguments and hypotheses Mr. Sollas has, with so much con- 

 fidence, based solely on evidence supplied by a shallow-water 

 cretaceous deposit like that of Trimmingham, subject as it 

 must have been to disturbing tidal and current-influences 

 during the period of its deposition, and to still more violent 

 and cataclysmal agencies afterwards, must be looked upon as 

 untenable. 



I will now proceed to consider two other important ques- 

 tions which have a direct bearing on the flint-formation. The 

 first is : — Does the ordinary theory of replacement of carbo- 

 nate of lime by silica, which has been so ably discussed by 



