For many years the acid solution of limestone samples has provided geologists with insoluble residues for study and correlation. These residues include some types of fossils not dissolved as rapidly as the limestone matrix. A series of studies in progress in the Kansas Geological Survey Laboratories on insoluble residue techniques and the recovery of phosphatic fossils from limestone, showed that etching and solution of the phosphatic fossils had begun before the fossils were completely freed from the limestone matrix. The chemical reaction between the acid and the fossils continued after the fossils had settled to the bottom of the beaker. This deleterious effect was observed to be sufficient to almost