SCIENCE IN SECONDARY SCHOOLS. 197 
cage. Considerations such as these make it desirable to know something of the 
soil. 
To grow plants properly, they must be cultivated; all soils are not equally 
good. What is soil? The surface crust of the earth. Even in those regions 
which consist of hard rock, the surface is usually soft soil formed by the 
gradual decay of the rock under the influence of the weather. What kinds of 
soft rock or soil do you know—what kinds of hard rock? 
The soft soil everywhere is either sand or clay or a mixture of these (loam). 
You probably know both kinds and are well aware that they are very different, 
but it is better that you should examine them carefully. Take grams of 
each, examine them—if possible with a magnifying lens; describe them, con- 
trast their behaviour, also their behaviour with water, both when wetted with 
it and when stirred up with a considerable quantity. Afterwards examine some 
garden and field soil and see what you can separate by stirring up the soil 
with water and decanting off the water before the lighter particles have 
settled. 
The separation of sand from clay is always going on in rivers and in many 
places along the sea-coast: and it is on this account that sand-banks are 
formed in rivers and that the sea-shore more often than not consists of sand. 
Sandstone.—Sand is found in many places mixed up with pebbles of various 
sizes—how are such rounded pebbles produced, do you suppose? If you have 
been on the sea-coast where there is a shingle beach, you will probably be able 
to account for the rounding of the pebbles. What are gravel pebbles like 
inside—do they in any way resemble sand? 
Hard rocks are of frequent occurrence which are obviously formed of sand 
particles stuck firmly together—these are commonly known as sandstones; they 
are usually coloured more or less—yellow, brown, or even bright red. Flint, 
chert and quartz are solid, somewhat glass-like vocks, which when broken into 
small pebbles give a material like sand. 
Clay.—In many places, soft rocks are found which are more or less easily 
split up into slabs or sheets; these are known as shales or slate rock. If the 
fine powder formed by grinding them be mixed with water, it forms a more or 
less sticky, clay-like mass. 
Timestones.—Rocks which yield lime when burnt are very generally met 
with together with sand and clay; they vary much in character according to 
the district, some being soft like chalk, others hard and crystalline like mountain 
limestone. The limestones are always full of fossils; chalk under the microscope 
appears to consist almost entirely of shell-like remains. 
Igneous rocks.—Sandstone, clay and limestone are known as sedimentary 
rocks—there being complete proof that they have been deposited as sediments 
from water. 
A fourth class of rock includes all rocks which have cooled down from the 
fused state. Granite is one of the most characteristic of these rocks and is 
well known, as it is much used as an ornamental stone for building. 
Iiveryone should be familiar with the common rocks and take some interest 
in their history : and the wonderful story they tell when properly interpreted : 
but this should be made almost entirely an outdoor occupation. 
Nature or LIMESTONE. 
In studying starch, we have taken into account things which were known 
about it and have based experiments on these: the results have enabled us to 
arrive at certain conclusions; our discovery that starch contains carbon and 
perhaps water was based on the study of the changes which it undergoes when 
heated and when burnt in air. We were led on to study the changes which 
metals undergo when burnt and to discover that the earthy substances into 
which they are converted are compounds of the metals with Fire air. We were 
able to take away the Fire air from the metal in some of the earths by means 
of carbon. In every case a change was effected—we arrived at our knowledge 
of the nature of the subiect by studying a change in which it was concerned. 
Can this method be applied to the study of soil materials—in appearance they 
resemble closely the earths obtained by burning metals—are any of them known 
