es of a great inland sea that covered the central portion of
North America. In the ages that followed, these rocks were covered
deeply with later sediments. But the upheavals of the crust have broken
open and erosion has uncovered these strata in different regions.
Geologists have found written there, page upon page, the record of life
as it existed in the early seas.

THE LIME ROCKS

"Hard" water and "soft" water are very different. The rain that falls
and fills our cisterns is not softer or more delightful to use than the
well water in some favoured regions. In it, soap makes beautiful, creamy
suds, and it is a real pleasure to put one's hands into it. But in hard
water soap seems to curdle, and some softening agent like borax has to
be added or the water will chap the hands. There is little satisfaction
in using water of this kind for any purpose.

Hard water was as soft as any when it fell from the sky; but the rain
water trickled into the ground and passed through rocks containing lime.
Some of this mineral was absorbed, for lime is readily soluble in water.
Clear though it may be, water that has lime in it has quite a different
feeling from rain water. Blow the breath into a basin of hard water, and
a milky appearance will be noted. The carbonic acid gas exhaled from the
lungs unites with the invisible lime, causing it to become visible
particles of carbonate of lime, which fall to the bottom of the basin.

Nearly all well water is hard. So is the water of lakes and rivers and
the ocean, for limestone is one of the most widely distributed rocks in
the surface of the earth. Rain water makes its way into the earth's
crust, absorbs mineral substances, and collects in springs which feed
brooks and rivers and lakes. Wells are holes in the ground which bore
into water-soaked strata of sand.

We gain something from the lime dissolved in hard water, for it is an
essential part of our food. We must drink a certain amount of water each
day to keep the body in perfect health. The lime in this water goes
chiefly to the building of our bones. Plant roots take up lime in the
water that mounts as sap through the plant bodies. We get some of the
lime we need in vegetable foods we eat.

All of the kingdom of vertebrate animals, from the lowest forms to the
highest, all of the shell-bearing animals of sea and land, require lime.
Many of the lower creatures especially these in the sea, such as corals
and their near rel