OlUGlN OF I IRONSTONES. 
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0. The combinations of peroxide of iron aro rod- 
dish-brown, for example, iron-rust, and 
ordinary burnt brick. 
7. Rain waters become carbonated on falling 
through the atmosphere, or on filtering 
through beds of decomposing vegetable 
matter. 
With those ascertained facts before us we can see 
for ourselves beds of ironstone in the course of forma- 
tion. Carbonic acid is given off everywhere in 
swampy thickets, from layers of fallen leaves, from 
decaying timber and tangled undergrowths. Vast 
quantities of the same gas aro given olf by volcanoes, 
and by mineral springs, such as the Soda, Springs near 
Cooma. The carbonic acid so abundantly available is 
taken up by water. Here, then, we have a solvent 
able to penetrate the pores, cracks, crevices, and joints 
of rocks, and seize upon all the protoxide of iron it 
meets in its passage. Laden now with its invisible 
load in solution, the water oozes from the soil, untli it 
collocts in some lagoon or ditch. Soon a film of the 
water in the lagoon, in contact with the air, absorbs 
additional oxygen from the atmosphere. The result 
is that the soluble and invisible protoxide becomes 
converted into a peroxide, which is both visible and 
insoluble. This shows itself as an iridescent scum 
floating on the water, not unlike a film of oil. Hut 
being a peroxide of iron and insoluble, it quickly sinks 
to the bottom of the lagoon as a reddish mud. A fresh 
