nse and compact and
in some regions is used for fuel.

HOW WERE SOILS MADE?

As a help in finding the answer to this question collect and examine a
number of the following or similar specimens:

_Brick._--Take pieces of brick and rub them together. A fine powder or
dust will be the result.

_Stones._--Rub together pieces of stone; the same result will follow,
except that the dust will be finer and will be produced with greater
difficulty because the stones are harder. Some stones will be found
which will grind others without being much affected themselves.

_Rock Salt or Cattle Salt._--This is a soft rock, easily broken. Place
on a slate or platter one or two pieces about the size of an egg or
the size of your fist. Slowly drop water on them till it runs down and
partly covers the slate, then set away till the water dries up. Fine
particles of salt will be found on the slate wherever the water ran
and dried. This is because the water dissolved some of the rock.

_Lime Stone._--This is harder. Crush two samples to a fine powder and
place one in water and the other in vinegar. Water has apparently no
effect on it, but small bubbles are seen to rise from the sample in
vinegar. The vinegar which is a weak acid is slowly dissolving the
rock. The chemists tell us water will also dissolve the limestone, but
very slowly. There are large areas of soil which are the refuse from
the dissolving of great masses of limestone.

We find that the rocks about us differ in hardness: they are ground to
powder when rubbed together, some are easily dissolved in water,
others are dissolved by weak acids.

Geologists tell us that the whole crust of the earth was at one time
made up of rocks, part of which have been broken down into coarse and
fine particles which form the gravel, sand and clay of our soils. The
organic matter of our soils has been added by the decay of plants and
animals. Several agencies have been active in this work of breaking
down the rocks and making soils of them. If we look about we can
perhaps see some of this work going on now.

_Work of the Sun._--Examine a crockery plate or dish that has been
many times in and out of a hot oven, noticing the little cracks all
over its surface. Most substances expand when they are heated and
contract when they are cooled. When the plate is placed in the oven
the surface heats faster than the inner parts, and cools faster when
taken out of the oven. The result is that the