ON A PIECE OF CHALK 49 



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 num- 

 ber of nearly globular chambers of different sizes 

 congregated together. It is called Globigerina, and 

 some specimens of chalk consist of little else than 

 Globigerince and granules. 



Let us fix our attention upon the Globigerina. It 

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

 learn what it is and what are the conditions of its ex- 

 istence, 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 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 out- 

 ward form of organic bodies so this mineral sub- 

 stance, 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 con- 

 ception is at present held to be admissible, it is be- 

 cause long and varied experience has now shown that 

 mineral matter never does assume the form and struc- 



