A graph showing the relation between maximum thallus diameter of Rhizocarpon geographicum and age of the individual is presented as an aid to detailed chronological studies in this section of the eastern Canadian Arctic. The curve is derived from: (1) historically dated surfaces; (2) measured growth of Alectoria minuscula for a two year period; (3) the inter-specific ratios of A. minuscula/R. geographicum; and (4) radiocarbon-dated surfaces associated with lichens. The size/age curve for R. geographicum shows an initial fast rate of growth of 0.15 mm yr−1 which falls off to approximately 0.03 mm yr1−1 after the passage of 250 to 300 yrs. Extrapolation of the curve back to about 9,500 B.P., when individual maximum thalli would be 280 mm in diameter, is in accord with independent geological dating. The linear growth phase of 0.03 mm yr−1 is remarkably similar to rates derived from the Colorado Front Range and the St. Elias Mountains, Alaska, and prompts speculation as to whether this particular lichen species may not have a single growth curve regardless of location. Contrary evidence is also presented.