120 
Geology of Sydney. 
quantity of protoxide now comes in contact with the 
air, to be in its turn converted into peroxide. This 
also sinks, as another layer of ironstone. The process 
continued gives us a bed of iron ore. 
Perhaps a fern frond, or a tiny leaf, lies below. It 
is soon buried in the accumulating iron mud, and this 
shows how the impress of fossil leaves are found in 
these ironstones. 
This explanation, it may be said, is satisfactory 
enough in theory, but how does it work in practice ? 
Perfectly. Go to any fresh-water lagoon in swampy 
country. You will soon discover the iridescent scum 
I have described. Water in theselagoons has an inky 
taste from the dissolved protoxide of iron. Standing 
by the water you are looking on one of the most beau- 
tiful, and for ages past, hidden processes that Nature 
has made use of through all time, to separate iron- 
stone into beds. We are not concerned with theory, 
as a matter of fact, some of the best Swedish steel is 
being manufactured from such deposits of iron ore, 
now forming in Swedish lakes. 
It only remains to add that the iron diffused in 
rocks and collected by carbonated waters need not 
necessarily be in the form of soluble protoxide. 
Nature has another simple and silent reaction unceas- 
ingly in operation, which is forcibly removing a 
portion of its oxygen from the insoluble peroxide, and 
so converting it into the soluble protoxide. 
