Forty-one well-dated fragments of bone from rocks of Tertiary age have been studied by X-ray emission spectrography methods. Fe, Sr, Ba, As, Y, Sb, La, In, and Mn have been detected, and variations in content of certain of the elements have been noted that appear related to the age of the samples. Older bone fragments contain considerably higher Fe and very little As; younger bone fragments contain lower Fe and high As. Combinations of elements also differ in bones of different ages. These variations seem independent of the species of animal studied, but may be dependent on environment of deposition. Preliminary results suggest that spectrographic analyses of bone fragments may be useful in stratigraphic correlation where fossils are too poorly preserved for identification.