The X-ray fluorescence method was used to analyze 113 shales; seven from the Upper Devonian Calmar Formation, 98 from the Lower Cretaceous Mannville Group and 8 from the Lower Cretaceous Joli Fou Formation. The average composition of the shales studied is 64.83% SiO2, 2.66% MgO, 15.72% Al2O3, 2.50% K2O, 2.42% CaO, 5.08% Fe2O3, 97 ppm. Rb, and 210 ppm Sr. The Rb/Sr ratio of .46 is in good agreement with that suggested for shales by earlier workers. The Rb/K varies from about 0.004 for shales formed in a brackish environment, to 0.006 for normal marine shales.