224 Scientific Intelligence. 
850,000,000 of years; and many more millions should be added 
for the continuation of the cooling down to 100° C.; all of which 
is surely very unsafe to conclude from the existence of those iron 
ore beds that the vegetation was extremely abundant, or that any 
then existed. 
Neither does the phosphate of lime (apatite), which is so gene- 
rally disseminated through the iron ores, afford good evidence of 
life. The amount of this mineral in Archean rocks exceeds that 
in all the later rocks of the globe, and would certainly indicate 
the existence of an extraordinary amount of life over the Archean 
marshes and lands if of any at all. Some of the earliest shells of 
the Silurian (Zingule and a few related kinds) consist largely of 
phosphate of lime, as shown by Hunt, and this appears to prove, 
as this author has observed, that the waters of the ocean then 
held in solution more phosphates than they now do. And the 
