One of the older known occurrences of euxenite in Ontario is that on lot 13, con. V, South Sherbrooke township, Lanark County, near the village of Maberly. This was first described by Willet G. Miller and Cyril W. Knight2 with an analysis by the Imperial Institute, London. This analysis. gave only a very small Pb/U+0.38 Th ratio and consequently indicated a very late age, perhaps Carboniferous for the pegmantite in which it occurs, a conclusion not in accord with the geological evidence as the dike appears to be no different in any way from many other middle Precambrian pegmantites of Ontario now known to be between 1100 and 1200 million years old. It should be noted, however, that Miller and Knight considered that there is evidence for the existence of a younger Precambrian granite3 in the ancient complex of central Ontario. The samples analyzed by the Imperial Institute came from the first superficial workings and quite likely were considerably leached and altered. As the writer subsequently obtained large quantities of very fine apparently fresh material from a depth of 30 to 40 feet, it was thought to be worth while to analyze a large average sample with a view to check the age of the pegmatite.