We use this special earth to clean out the bath tub and scour the sink. There may be some of it even in our toothpaste. In industry, diatomaceous earth is used as a filter to sift out particles of impurities from fluids and syrups. There is a clue to its nature in the word diatom, which is the name of countless small waste dwelling members of the plant world.

Diatomaceous earth is made of hard and gritty particles, so small and fine that the substance feels smooth to the touch. This is one reason why it makes a wonderful cleaning agent   it scrapes off the dirt without scraping the smooth face of the suing porcelain in the wash basin.

The diatomaceous earth in cleansing powders is a gift of the plant world. Its tiny, gritty particles were made by diatoms which teemed in the ancient seas millions of years ago. There have been diatoms for a hundred million years and they still thrive in salt and dishwater all over the world.

It is sad that the diatoms are too small for our eyes to see, for they are like fairy jewel boxes, each one more beautiful than the next. Most of them measure about one thousand to an inch. They are microscopic relatives of the water loving algae, including the various seaweeds.

Each diatom is a tiny, yellowish brown body inside a pain of matching shells. It has green chlorophyll which it. uses to make plant color. 'The shells are made from silica, one of the hardest of tr o natural minerals.

The twin shells which encase the diatom are held together with a thin girdle around the waist. They may be shaped like buttons or squares, oblongs or diamonds, stars or sticks. But each little box is sure to be ornately ornamented with a design of ridges and grooves or humps and hollows or spikes and buttons.

In the remote past, countless trillions of diatoms lived and died and their dainty shells sifted to the oozy floor of the seas. When stretches of shallow seas dried up, the old sea beds became layers of diatomaceous earth.

Some 15 million years ago, what is now central California was flooded by shallow seas. Countless trillions of tiny diatoms lived and died in the sunny waters, adding piles of microscopic shells to the sea bed. Later the area became dry land and gritty diatom shells were mixed with the rich soil. In places where the shells are concentrated, the diatomaceous earth is mined to make cleansing powder.