1 Fes., 1902.] QUEENSLAND AGRICULTURAL JOURNAL. 75 
contains only two substances, silica and alumina. Perhaps you have seen 
bright, golden-looking ornaments in shop windows, and you are told they 
are made of aluminium. Well, it is from clay that this bright metal 
is obtained. Now, this pure clay would be quite useless for agricultural 
purposes, but generally it has been discovered by chemists that clay 
contains many things which are useful as plant food, such as potassium and 
magnesium, so that a clay soil may be made to produce crops which would be 
impossible on a soil consisting of pure sand, notwithstanding its being cold and 
wet, owing to its retentive nature. It is also valuable on account of its being 
able to take in and preserve the substances produced by the decomposition of 
manure. 
Another and a very important constituent of the soil is CarBonarE oF 
Lime, so called because it is a compound of lime with our old friend carbonic 
acid. Farmers put lime upon the land because it helps to decompose stable 
manure, and when organic manures are decomposed they add other plant foods 
to the soil. 
Now you see that pure clay and pure sand are of little value to the farmer 
unless he does something to them by which he can render them fertile. Thus 
they require more plant food to be added to them in the shape of manure. 
Clay lands, in addition to this, require to be drained, otherwise the rain water 
would not be able to get away. It would become stagnant, and the clay soil 
would remain cold, and all the manure in the world would not help the plants 
if their roots were resting on the cold, wet bottom. In our next lesson we will 
endeavour to learn something about manures and about the reasons for 
manuring. 
Questions on Lesson 11. 
1. What is meant by the constituents of a soil ? 
2. Describe an experiment illustrating the fact of water being contained 
in a soil. 
3. Distinguish between a soil of pure sand, of sandy loam, and of clay. 
How do they differ from each other ? 
. How do you find out what soluble constituents are contained in a soil ? 
. Name a soluble and an insoluble constituent of a soil. 
. What is the meaning of the term ‘“‘ weathering ” ? 
. How does a sterile soil like sand become fertile ? 
. Give an instance of pure sea-sand developing into great fertility. 
. What is sand? Clay? 
. How does micaceous sand differ from pure sand ? 
11. What plant food does mica provide ? 
12. Of what value is sand when mixed with a heavy soil ? 
13. What is silica? What is alumina ? 
14. How does pure clay differ from impure clay ? 
15. What is carbonate of lime? Of what value is it in agriculture ? 
16. Why do clay lands require to be drained ? 
i 
SMOONODONE 
121m Lesson. 
SECOND STAGE, 
_ In the first lesson of this book, you learned a little more about soils than I 
had already told you, and you discovered that some are naturally fertile—for 
instance, those which contain a large proportion of organic matter, and are thus 
almost entirely composed of humus, whilst others with a less rich supply are 
less fertile, such as sandy loams. Then came the least fertile soils, such as 
the cold, stiff, wet clays, and soils composed of pure sand. There are other 
