ABSTRACT IT HAS been generally accepted that chickens benefit from the use of a grinding agent, or grit, when fed whole or cracked grain in their diets. Laying hens also require abundant calcium for maximum egg production. This is usually provided by feeding calcium carbonate in the form of crushed oyster shells or limestone ad libitum. This method of providing calcium was tested by Heuser and Norris (1946a) and found to be more effective than the inclusion of ground limestone in the ration. Whether a material such as crushed limestone which apparently is sufficiently soluble in the digestive tract to provide adequate calcium can still serve as an effective grinding agent is controversial. These same workers (Heuser and Norris, 1946a) noted that the feeding of granite grit in addition to oyster shells or calcite grit appeared to have a favorable effect on egg production, feed efficiency, and shell strength. Scott and . . .