438 Mr. W. J. Sollas on the Flint 



sea mud differs from chalk in many important particulars, 

 yet still it is sufficiently related to warrant a comparison. 

 Since the remains of siliceous organisms are absent from the 

 chalk, but flints present, whilst in the deep-sea mud siliceous 

 organisms are abundant and flints absent, probably the mate- 

 rial of the flints had been to a greater or less extent derived 

 from these organisms." 



This argument depends on the analogy of some deep-sea 

 mud with the chalk ; and by this analogy the inference is 

 drawn that siliceous organisms were at one time present in 

 the chalk, just as they are now in the grey ooze. We shall 

 now proceed to make this inference independent of analogy 

 by showing that it is really nothing less than a statement of 

 fact. 



2. The deposits in which flints occur can be proved by 

 direct observation to have originally contained abundant sili- 

 ceous organisms, which have since, to a greater or less extent, 

 disappeared from them. 



The Trimmingham flints afford evidence straight to the 

 point ; for not only are sponge-spicules intimately associated 

 with them and in great numbers, but these spicules afford us 

 clear proof of the previous existence of a great mass of other 

 spicules of which they are themselves but a miserable rem- 

 nant. The small fragments of Hexactinellid and Lithistid 

 network indicate the previous existence of whole skeletons of 

 such network, and also of a great quantity of those minute 

 spicules which in the living sponge are thickly strewn through- 

 out its sarcode ; of these flesh-spicules not a trace is now to be 

 found. And finally, while a large part of the larger spicules 

 and all the flesh-spicules of the sponges have entirely disap- 

 peared, those that remain present abundant signs of corro- 

 sion, and have evidently lost a considerable proportion of the 

 silica they once contained. 



We thus see, not only that certain spicules still exist in the 

 flint-bearing chalk, but that, by the law of association, a 

 vastly greater number of other spicules must have existed 

 along with them. Somehow these other spicules cannot be 

 found in the deposit now ; somehow flint nodules, which are 

 not associated with recent sponges, have made their appear- 

 ance. And the inference is clear ; as one says, the facts speak 

 for themselves. 



This argument holds not only in the case of the Trimming- 

 ham flints, but of nearly all flints which I have examined, 

 and may be extended to many other kinds of siliceous deposits 

 as well. In the Niagara chert-beds of the Silurian of North 

 America remnants of sponge-skeletons abound. In the Car- 



