Answer:

Good grit should consist of a hard, flinty substance in irregular shaped particles with sharp edges or corners.

For adult fowls the particles should be about the size of a pea or small bean. Round or smooth objects are worthless.

Crushed stone, gravel or broken chinaware is serviceable. Broken glass is sometimes used, but is not suitable, chiefly on account of possible injury from cutting the fowl internally. Mica Crystal grit, usually obtainable from any supply dealer, is a most excellent article.

A plentiful supply of good grit should always be within reach of fowls. It is necessary in aiding the action of the gizzard in grinding the food preparatory to digestion, and the lack of it is the foundation of many fatal ailments.