74, QUEENSLAND AGRICULTURAL JOURNAL. [1 Frs., 1902. 
alum, and salt which we dissolved during one of our earlier lessons. Those 
parts that cannot be dissolved in water are called zrsoluble, and these constitute 
the larger part of every soil, except in the case of some of our serub soils, which 
are almost entirely composed of organic matter. The insoluble parts are those 
which, as I explained, are derived from the crumbling of rocks, by the process 
called “‘weathering.”’ Weathering is a term used by geologists to indicate the 
crumbling of rocks by the action of the atmosphere and of water. 
Let us now study more closely the composition of soils. All soils you 
have long since discovered are originally derived from the solid rocks. I have 
told you how these rocks are decayed. They furnish the insoluble mineral 
matter of the soil. If nothing else were added to it, only the very lowest 
forms of vegetation could find any plant food in it. But these lower forms 
consist of mosses, lichens, and other humble organisms which botanists 
describe, and make such an amount of humus by their decay that higher 
forms of vegetable and also of animal life find a congenial home in it, and 
these again add still more to the plant food, until, finally, there is a deep rich 
soil formed which is able to support the higher types of the vegetable world. 
The islands of the South Seas, which are peopled by many black races, some of 
whom you see in Queensland working on the sugar plantations, were, many of 
them, nothing but heaps of coral and sea-sand. ‘There was no vegetation at all. 
But, by and by, some cocoanuts from other islands came floating along, borne 
on the currents of the sea, and were left by the side on the beach. Then bits 
of timber, logs, and seaweed, dead fish, dead birds, and other animals became 
stranded in the same place, and all these substances gradually decayed and 
formed “humus.’”’ The cocoanuts and other stranded seeds then sprouted and 
grew, and in course of years they spread over the whole island, and the fallen 
leaves, trunks, and nuts formed a rich coating of soil over the coral and sand ; 
and thus from a barren island there was formed a fertile one, on which man 
many years afterwards was able to settle down and get a living from the fruits 
of the earth. 
On such islands lime or, rather, limestone and sand are most abundant, 
but in older soils clay and also sand are present in the greatest quantity, 
although a certain amount of limestone is also found with them. 
We will now consider the various kinds of soil, but from a higher stand- 
point than that given you in your early lessons in agriculture. 
Sanp.—Sand is nothing but finely broken-up stone. Try pouring water on 
sand. You see that it passes away at once; and if the sand were 20 feet 
deep, the water would go right through it. Onsuch a soil, if we may call pure 
sand a soil, nothing can grow—that is to say, no field crops can grow. But 
there are certain running grasses which derive nearly all their nourishment 
from the air, which will grow on pure sea-sand, and are most useful in binding 
it together, and in forming humus for higher forms of plant life. But we are 
now considering farm soils, and, as a farm soil, sand is valueless, because it 
cannot furnish plant food. There is, however, one kind of sand which you may 
have noticed contains shiny glittering particles. These are a mineral called 
mica, and such sands are called mrcaczous. Now, mica, when it has decayed, 
provides several useful plant foods, such as potash, lime, and iron. Then there 
is another thing to be said in favour of sand. Although it has no value alone 
as a soil, yet it is very useful when it is mixed with heavy, stiff, cold soils. It 
makes them lighter, and when the hot sun shines on such soils its rays warm 
the sandy particles, and thus the cold soil is also warmed, and is rendered 
more suitable for producing farm crops. 
Cray.—In a former lesson it was explained to you that when clay forms 
the subsoil rain water rests on it—it will not pass through it. Such a soil is 
called impermeable. Now, how does clay differ from sand in its composition ? 
You have no doubt seen pieces of white stone called “quartz.” This quartz 
consists of what is called “ silica,’ and sand is a form of silica. Clay, on the 
other hand, contains other things besides silica, although the purest clay 
