A new estimate of the surface composition of exposed parts of the Canadian Precambrian Shield has been obtained, using samples of 122 rocks from northern Quebec–Ungava, 116 from Baffin Island, 116 from southwestern Quebec, 64 from northeastern Alberta, 18 from northern Saskatchewan, and 8076 from northern Ontario. Where feasible an interpenetrating replicate sampling design was used, with probability weighting by rock-type, analyzing both individuals and composites for trace elements, but only composites for major elements, A total of 385 triplicate spectrographic analyses and 48 major-element analyses were made.Regional differences between the six samples were detected; whether these also include secular variations could not be studied. The overall estimate follows:graphicThe major elements are similar to those found in granditorite, mica paragneiss, or graywacke, but the trace elements agree better with the last two only. Data for Th and U will follow later.The Precambrian Shield of Canada (and Fennoscandia also) contains more Si and K, and less Ti, Fe, Mn, Mg, and Ca than recent estimates of the whole crust of the earth.

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