The Message of Science. 23 



The present development of life on the earth began in 

 the age which geologists term the Silurian ; but the 

 presence of graphite in the Laurentian, or "azoic " rocks 

 renders it not incredible that there was a previous life 

 development which terminated, or was followed by a 

 period of high temperature. 



But to return to what is known, keeping it separate 

 from conjecture, we find that low forms of unicellular 

 life were existing on the earth many millions of years 

 ago. Geology affords the evidence of this, though the 

 exact number of millions of years is still debatable. That 

 is not material to our purpose, however ; it was a very 

 long time ago. Fire, water, and unicellular life have 

 wrought together to make the earth's surface what we 

 find it to-day. But geologists are agreed that there was 

 an azoic, or lifeless age, followed by an epoch when 

 protozoons — vegetable and animal cells of life, the 

 monera, protamoebidse, diatoms, algae, myxopods, rhizo- 

 pods, ciliata, flagellata, et al, — had appeared; unicellular 

 creatures from one ten-thousandth to a hundredth of an 

 inch in diameter. 



For millions, perhaps hundreds of millions of years, 

 certain of these protozoons were the sole inhabitants of the 

 earth which was fit for no higher form of life ; or, if fit, 

 no higher form had developed. Nothing more graphically 

 illustrates the wealth of time at Nature's disposal, or the 

 fact that the course of nature cannot be judged by human 



