Previous sulfur isotope data for the Lower Devonian Bear Rock Formation and the Upper Cambrian Saline River Formation in the District of Mackenzie, N.W.T. have been supplemented by additional sulfur isotope analyses as well as δ18O determinations on sulfates from outcrops, drill cuttings, and cores. Whereas the mean δ34S value for the Bear Rock Formation is lower than that of the Saline River Formation (+17.8 ± 1.8‰ versus +29.7 ± 2.2‰), the opposite trend was found for the mean δ18O values (+15.6 ± 1.0‰ versus +13.0 ± 1.5‰). The new data confirm that, for all samples analysed, there is no overlap between δ34S values for the two formations, while the δ18O data display some overlap. The earlier δ34S data for samples from an evaporitic section on the northeast side of the Norman Range (originally mapped as consisting entirely of Saline River Formation) indicated the presence of a thrust fault in the section, with Saline River strata overlying Bear Rock strata. The δ18O data for those samples, which fortuitously fall into two non-overlapping groups, confirm the earlier conclusions based on the δ34S data and allow us to define the position of the thrust-fault contact somewhat more closely.