10 The Origin of the 



also around them. For the flint Echinites, which, 

 when separated from the matrix of the flint in which 

 they have lain, may seem like mysterious organic 

 growths, formed by chemical substitution of flint, 

 present a very different account of themselves, when 

 undetached from the mass in which they have been. 

 The flint mass in a fluid or gelatinous state has 

 flowed round and eufolded the shell, and has also 

 penetrated into it, entering by a small orifice, so 

 filling it and moulding itself there. But its forma- 

 tion is destitute of any organic process, or affinity 

 for such. This may not be known to many of those 

 who have only seeu the specimens when detached, 

 but specimens undetached can easily be produced in 

 illustration. 



As regards the fluidity of the Silex, we know that 

 it might arise either from fusion by intense heat, or 

 by aqueous solution. The question is, Which ? And 

 here we premise that it is not necessary nor even 

 allowable to assume that the same method of fluid 

 formation applies both to flint and chalcedony or 

 quartz ; nor yet that all petrifactions have been 

 formed by the same process. They may have the 

 material of silex in common, but they may and do 

 differ in formation and in texture. At present we 

 confine our attention to the flint in connection with 

 the chalk. 



Some specimens, as has been sa : d, are of the sea- 

 shore ; and undoubtedly many occur from the sea 

 itself, some containing corals which had transfixed 

 them, while soft, and been broken off in their fall. 

 But it does not follow that in these cases the flint 

 owes it origin to the sea, or was formed under it. 

 The contrary is attested not only by some of the 

 facts already referred to, but still more by other facts 



