The grouping of areas of outcrop of Lower Silurian reefs along a stretch of the Attawapiskat River west of James Bay (northern Ontario, Canada) is controlled by a conjugate set of faults striking approximately 60 and 280°. The faults are evident in disturbed outcrops along the river and in subtle lineaments revealed in aerial photographs and Landsat imagery in the surrounding marshland topography. Slumping of large blocks from a reef crest in Silurian time and stratigraphic relationships within the Hudson Basin indicate a major episode of movement in late Llandovery time. Movements on the fault set have been traced back to Proterozoic time and, to affect the present subdued topography recently emerged from marine inundation, must have been renewed in rapid recent postglacial uplift of this area.

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