Peat is also largely vegetable matter, consisting of tough roots, partially decayed leaves, moss, etc.  It is quite dense 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 there is unequal expansion and contraction in the plate and consequently tension or pulling of its parts against each other.  The weaker part gives way and a crack appears.  If hot water is put into a thick glass tumbler or bottle, the inner surface heats and expands