54 TOILERS IN THE SEA. 



less in bulk than the original quantity of chalk 

 experimented upon, but it will contain just what is 

 required for microscopical examination. If we take 

 a little of this sediment, and place it on a slip of 

 glass, then submit it to the microscope, we shall 

 find it to be composed almost entirely of delicate 

 little shells, those called Globigerina predominating. 

 These shells are carbonate of lime, easily dissolved 

 by acids, the empty, untenanted houses of Fora- 

 minifera. That which has been washed away in the 

 Avashing process consisted partly of the broken frag- 

 ments of similar shells, and partly of amorphous 

 granules. Hence, therefore, the microscope teaches 

 that chalk consists, for the most part, of very minute 

 shells and fragments of shells, which were inhabited 

 by animals that lived and floated in the ocean thous- 

 ands of years ago. By their identity of size and 

 form, it is not difficult to recognise in them the shells 

 of Foraminifera, belonging to precisely the same 

 .species, in some cases, as those which are found 

 living at the bottom of the sea in the present day. 



D'Orbigny computed that there were near four 

 millions of such little shells in one ounce of sand from 

 the Antilles. According to this computation a cube 

 of chalk of six inches in diameter in each direction, 

 and weighing sixteen pounds, would contain the 

 -entire shells of not less than 1,024 millions of little 

 animals, and the broken fragments of nearly as 



