8 ON A PIECE OF CHALK i 



A suggestion which may naturally enough pre- 

 sent itself is, that these curious bodies are the 

 result of some process of aggregation which has 

 taken place in the carbonate of lime ; that, just 

 as in winter, the rime on our windows simulates 

 the most delicate and elegantly arborescent foliage 

 proving that the mere mineral water may, 

 under certain conditions, assume the outward 

 form of organic bodies so this mineral substance, 

 carbonate of lime, hidden away in the bowels of 

 the earth, has taken the shape of these chambered 

 bodies. I am not raising a merely fanciful and 

 unreal objection. Very learned men, in former 

 days, have even entertained the notion that all the 

 formed things found in rocks are of this nature ; 

 and if no such conception is at present held to be 

 admissible, it is because long and varied ex- 

 perience has now shown that mineral matter 

 never does assume the form and structure we find 

 in fossils. If any one were to try to persuade 

 you that an oyster-shell (which is also chiefly 

 composed of carbonate of lime) had crystallized 

 out of sea-water, I suppose you would laugh at 

 the absurdity. Your laughter would be justified 

 by the fact that all experience tends to show that 

 oyster-shells are formed by the agency of oysters, 

 and in no other way. And if there were no better 

 reasons, we should be justified, on like grounds, 

 in believing that Glolrigerina is not the product of 

 anything but vital activity. 



