THE DAWN-ANJMAL AS A TEACHER IN SCIENCE. 223 



indirectly products of the action of life. Wlien 

 the recent deposits discovered by the Challenger 

 dredgings shall have been more fully examined, we 

 may perhaps have the means of distinguishing such 

 rocks, and thus of still further enlarging our concep- 

 tions of the part played by Protozoa in the drama 

 of the earth's history. In any case it seems plain 

 that beds of greensand and similar hydrous silicates 

 may be the residue of thick deposits of foramini- 

 feral limestone or chalky matter,, and that these 

 silicates may in their turn be oxidised and decomposed, 

 leaving beds of apparently inorganic clay. Such 

 beds may finally be consolidated and rendered crys- 

 talline by metamorphism, and thus a great variety 

 of silicated rocks may result, retaining little or no 

 indication of any connection with the agency of life. 

 We can scarcely yet conjecture the amount of light 

 which these new facts may eventually throw on the 

 serpentine and other rocks of the Eozoic age. In the 

 meantime they open up a noble field to chemists and 

 microscopists. 



When the marvellous results of recent deep-sea 

 dredgings were first made known, and it was found 

 that chalky foraminiferal earth is yet accumulating in 

 the Atlantic, with sponges and sea urchins resembling 

 in many respects those whose remains exist in the 

 chalk, the -fact was expressed by the statement that we 

 still live in the chalk period. Thus stated the con- 

 clusion is scarcely correct. We do not live in the 

 chalk period, but the conditions of the chalk period 



