crumbled granite, the rocky foundations of
the earth.

METAMORPHIC ROCKS

In the dawn of life on the earth, soft-bodied creatures, lowest in the
scale of being, inhabited the sea. The ancient volcanoes the
subterranean eruptions of which had spread layers of mineral substance
on the ocean floor, and heated the water to a high degree, had subsided.
The ocean was sufficiently cool to maintain life. The land was being
worn down, and its debris washed into the ocean. The first sand-banks
were accumulating along sandy shores. The finer sediment was carried
farther out and deposited as mud-banks. These were buried under later
deposits, and finally, by the rising of the earth's crust, they became
dry land. Time and pressure converted the sand-banks into sandstones;
the mud-banks into clay. The remains of living creatures utterly
disappeared, for they had no hard parts to be preserved as fossils.

The shrinking of the earth's crust had crumpled into folds of the utmost
complexity those horizontal layers of lava rock poured out on the ocean
floor. Next, the same forces attacked the thick rock layers formed out
of sediment--the aqueous or water-formed sandstones and clays.

The core of the globe contracts, and the force that crumples the crust
to fit the core generates heat. The alkaline water in the rocks joins
with the heat produced by the crumpling and crushing forces, acting
downward, and from the sides, to transform pure sandstone into glassy
quartzite, and clay into slate. In other words, water-formed rocks are
baked until they become fire-formed rocks. They are what the geologist
calls _metamorphic_, which means _changed_.

In many mountainous regions there are breaks through the strata of
sandstone and slates and limestones, through which streams of lava have
poured forth from the heated interior. Along the sides of these fissures
the hot lava has changed all the rocks it touched. The heat of the
volcanic rock matter has melted the silica in the sand, which has
hardened again into a crystalline substance like glass.

Have you ever visited a brick-yard? Here men are sifting clay dug out of
a pit or the side of a hill, adding sand from a sand-bank, and in a big
mixing box, stirring these two "dry ingredients" with water into a thick
paste. This dough is moulded into bricks, sun-dried, and then baked in
kilns themselves built of bricks. At the end of the baking, the soft,
doughy clay block is transformed into a