STRATIFIED OR SEDIMENTARY ROCKS MESOT 
Origin. Place a few pieces of hard igneous rock in a 
bag and shake up for a few minutes; open the bag and 
ascertain that particles have been broken off. Educe that 
rocks tumble into the sea or into rivers and are rubbed 
against each other until they are ground to pieces—that 
the softer minerals are either dissolved or reduced to mud 
and carried away—and that the harder minerals alone 
remain. Refer to lesson on Quartz, note that it is the 
hardest of all the minerals examined, and explain that it is 
one of the commonest rock-forming minerals, and hence 
that it is not surprising to find it in such quantities in sea 
and river-sand. 
Mix up some gravel, fine and coarse sand ; empty this 
into a wide jar containing water and, after shaking up the 
contents, allow the whole to settle. Notice that the solid 
particles have arranged themselves in definite layers, the 
coarsest and heaviest at the bottom and the finest and 
lightest on the top, Explain that rivers and currents carry 
the sand and spread it over the sea-floor where it settles 
down in definite layers, and where partly by the pressure 
of the deposit itself and partly owing to the cementing 
material which gradually finds its way into the mass and 
unites the grains, the whole is cemented into rock. 
Explain the meaning of the term sedimentary. Explain 
further that the crust of the earth is undergoing slow and 
continuous movement, that some parts are being depressed 
or lowered, and others are being upraised ; that the layers 
of Sandstone laid down on the sea-floor in ages past have 
been elevated above the sea level until they have become 
dry land. Recapitulate reasons for supposing Sandstone to 
be a rock of aqueous origin. 
(a) Composed of grains similar in all respects to sea or 
river-sand. 
