How Chalk is Made 



same kind of sheltering skeletons. Some con- 

 struct delicate domes or many-chambered discs 

 of sand-grains, joined together with enough 

 carbonate -of- lime to act as building -cement. 

 Such skeletons are called " tests," to distinguish 

 them from " shells" proper. 



Hardly anything can be more remarkable than 

 the way in which these tests are put together 

 by mere specks of jelly, alive indeed, but without 

 parts, without development, without understand- 

 ing. How and why they should choose from 

 one place, each the especial materials which go 

 to form its own kind of " test," is one of the 

 mysteries in Nature for which Science has no 

 explanation. We can but look and marvel. 



One kind of jelly-speck will use the larger 

 grains of quartz, arranging them, and joining 

 them into a bottle-shaped test or shelter. 



Another, in the same spot, belonging to a 

 different species, will select tinier grains of the 

 same substance, and will build out of them a 

 rounded sphere, exquisitely modelled, with tiny 

 holes at intervals for the protruding " limbs." 



Another, of yet a different species, picks out 

 the minutest of sand-grains and of bits of 

 sponge-spicules, and knits them together, with- 

 out any cement, into delicate white globes, "like 



L 145 



