1 Nov., 1901.] QUEENSLAND AGRICULTURAL JOURNAL. 455 
carbon would have been burnt to a white ash, and a poisonous gas would have 
escaped into the air. This gas is cARBonrc acrp Gas, and is the one I told you 
about in a former lesson as entering so largely into the composition of the 
plant. Indeed, the black charcoal is nothing but the carbon which was taken 
up by the tree when it was growing, in the form of carbonic acid gas. 
Now we have these three gases operating upon the rocks, in the first 
instance, to assist in producing earth or soul, Oxygen has an unpleasant habit 
of attacking any metal exposed to its influence. Jf you leave your knife out 
on the grass for a night or so, what do you notice if you are so lucky as to find 
itagain? It is all “rusty,” you say. That is the work of Mr. Oxygen, backed 
up by his friend Mr. Carbonic Acid. But you say you can rub the rust off. 
So you can, but that rust is a part of the metal of your knife, and if you left 
it too long in the care of our two friends, Oxygen and Carbonie Acid, you 
would, in the end, have no knife left. They would have eaten it completely up. 
But these two fellows, if they are troublesome in the way of damaging our 
knives and agricultural implements left out in the field, do splendid work in 
making a soil. They eat into the rocks, which slowly crumble under their 
attacks, and are themselves helped in the work of destruction by heat, by frost, 
and by the swelling roots of trees. The water collected in the holes, where 
certain minerals contained in the rock have been eaten away, freezes, and as 
water, in freezing, expands, the rocks are burst asunder. If ever you go to 
Europe and go into a pine forest in winter, when everywhere there is a covering 
of ice and snow, you will hear loud reports-all round you. It is the sound of 
the trees bursting owing to the force of the frozen sap. (When water begins 
to freeze it takes up more room at first—that is, it swells.) 
Well, then, I have shown you how a soil is created. I have also shown you 
that the soil so formed contains much of the food requisite for plants, and that 
it is rendered available for them by its being roused from a dormant to an 
active state, by means of the gases we have been just talking about, together with 
a few others, which I will not tell you of now, because in a future lesson, and 
when you are better able to understand me, I shall explain to you all about 
the various plant foods. 
Let us now consider some of the soils which we can see around us. I 
mean, let us consider their fertility. By fertility, you must understand, is 
meant their hoiding more or less available plant food. Let us once more 
consider the scrub soils, and the soils of the Darling Downs, and of other great 
fertile plains in the State. Ina sense you would be right in saying that these 
soils are fertile, but there are scrub soils which possess very little fertility, and 
there are lands on the Darling Downs which are actually injurious to plant 
life. However, let us agree that scrub soils, as a rule, are very fertile; but 
what makes them so? You remember, of course, what the scrub soils are 
composed of, and to further explain this I must get you to remember another 
word you have never heard before. That word is HUMUS, or ORGANIC MATTER. 
You have seen a heap of sand, or white quartz, or gravel? Very good. The 
name given to that is, ¢organic matter. You have moved a heap of dead 
leaves or a bit of rotten bark, and have seen a dark-brown substance covering 
the ground beneath them? ‘That is organic matter or humus. Now let us 
understand what is meant by the terms organic matter and inorganic matter. 
Organic matter is so called because it is composed of the remains of plants 
or animals provided with ‘‘ organs” of life, such ays veins, pores, limbs, leaves, 
skin or bark, hair, &e. 
Inorganic matter is that which has no life, which has no organs—such as 
rocks, metals, minerals, and precious stones. ‘The former contains most of the 
necessary plant foods; the latter may contain some plant foods, but they are 
dormant, as I told you, until, as is the case of the lime, they are roused to 
activity by the addition of some other substance. 
However, we will not now trouble ourselves about these dormant plant 
foods, but will let them sleep on and get to know something about the various 
plant foods contained in the organic matter we spoke about, and then you will 
