of the Flints of the Upper Chalk. 307 



In Dr. Turner's lecture (p. 27) he says, " The development of 

 regular crystals was owing to the extremely slow progress of the 

 same process which, when less slow, might cause the deposits to 

 be amorphous/^ This precisely accords with the view suggested 

 of the rapid solidification of the amorphous flint round the living 

 animal, and the slow deposit of the crystallized silex * in the 

 subsequently present hollow space. 



Of course cases occur in which other substances besides chal- 

 cedony have insinuated themselves into the hollow.. Such cases — 

 the line of division being equally marked — serve only further to 

 illustrate my position. In the majority of cases however it is 

 chalcedony. 



To these observations on this first point I will add nothing 

 more at present but the remark, that the suggestion offered in 

 my former paper (p. 4) as explanatory of the presence of fray- 

 merits of sponge tissues in many flints has a strong light thrown 

 on it by these observations, and the bearing of these observations 

 on the present question becomes of great importance when those 

 fragments are considered. I there considered them to be torn 

 fragments of the horny tissue. In such case it is clear that 

 none of the gelatinous substance of the sponge would be pre- 

 sent. It would be purely and truly a mere fragment of the 

 horny network. Consequently this would be indeed saturated 

 with and imbedded in the flint itself, and, there being no gela- 

 tinous mass to decompose, no hollow space would ever be left to 

 be filled with chalcedony. Hence if is that around sitch tissues we 

 see none of the semitransparent chalcedony, but simply the dull 

 homogeneous flint. Hence the true nature and origin of those 

 fragments, as suggested in p. 4, is — with the consistency which 

 always attends the examination of new facts by the light of 

 a true explanation of nature — rendered almost demonstrative, 

 and, by consequence, the so-called " characteristic flint tissue '' 

 at once placed out of further question and removed altogether 

 from the argument. And yet it is upon the presence of these 

 fragments only that the whole fabric of the sponge theory has 

 been raised ! Even the weak analogy which they afforded, and 

 on which the whole ^^ anticipation '' rested, seems thus entirely 

 destroyed ; and the facts which destroy it appear to increase the 

 light which points with clearness to the true origin of the modes 

 and forms in which the flints of the upper chalk are actually found, 



* For convenience this move transparent part may be termed chalcedony, 

 though it is clear that chalcedony and flint are merely different forms of 

 silex, having a differing amount of foreign matter and impurities. The 

 gaseous state of the chalcedony would tend to cause it to have less of the 

 grosser impurities which discolour the flint and render it opake. Hence its 

 general transparency. 



22* 



