ix.] ON A PIECE OF CHALK. 179 



separated from one another, and submitted to micro- 

 scopic examination, either as opaque or as transparent 

 objects. By combining the views obtained in these 

 various methods, each of the rounded bodies may be 

 proved to be a beautifully-constructed calcareous fabric, 

 made up of a number of chambers, communicating freely 

 with one another. The chambered bodies are of various 

 forms. One of the commonest is something like a 

 badly-grown raspberry, being formed of a number of 

 nearly globular chambers of different sizes congregated 

 together. It is called Globigcrina, and some specimens 

 of chalk consist of little else than Globigcrince and 

 granules. 



Let us fix our attention upon the Globigcrina. It is 

 the spoor of the game we are tracking. If we can learn 

 what it is and what are the conditions of its existence, 

 we shall see our way to the origin and past history of 

 the chalk. 



A suggestion which may naturally enough present 

 itself is, that these curious bodies arc 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 

 experience has now shown that mineral matter never 

 docs assume the form and structure we find in fossils. 



