732 Noshkin et al. Fig. 3. Demonstration X-radiograph of a coral section. Annual band boundaries (not all necessarily evident on this exposure) are identified. Wedge outlines the section removed for radionuclide analysis. energies. Regions of the developed autoradiography film revealed inclusions of radioactivity (Fig. 2: these bands are darkened for better contrast). Three distinct bands near the base of the coral can be identified with the test series years 1954, 1956, and 1958; they are 15, 14, and 12.5 em from the o coral surface. These measurements gave average growth rates of 0.81, 0.85, and 0.87 cm yr? between 1954, 1956, 1958, respec- tively, and 1972. The distance between the 1954 and 1958 bands, however, is only 2.5 cm, yielding an average growth rate during this period of only 0.6 cm yr. The annual skeletal layers are not of constant thickness; in assigning the annual boundaries to posttest growth, werelied on the density variations in the exposed X-ray film. Figure 3 shows one exposed X-ray film of the coral section. Careful examination reveals alternating light and dark bands in the skeletal matrix. Several exposures were examined before a complete selection of annual band “boundaries” could be made. Buddemeier et al. (1974) concluded that the low-density band (dark X-ray negative) is correlated with a growth period beginning around December or January and ending aroundJuly. In our sample, the three bands in the autoradiograph of vt avoid possible contamination.) Vertical subsections 2 cm thick were cut from the facing coral halves. Oneslice, chosen for autoradiography, was placed in direct contact with No-screen-X-ray film for 60 days; the adjacent slice was subjected to X-radiography, with several exposures at different