The bulk of the strata are arenaceous: medium- to fine-grained, submature, subarkose to arkose; some are calcareous (Espanola Formation). The Bruce and Gowganda Formations are pebbly, conglomeratic muddy sandstone in which the 'matrix' generally is fine-grained subarkose, locally lithic. Paleocurrent study based on cross-bedding azimuths and dimensional fabric of phenoclasts suggests that the sediment transport for all the Huronian formations in this area was persistently from the north-northeast and north-northwest quadrants. Most arenaceous rock types are coastal plain fluvial deposits probably laid down by a system of migrating meandering rivers. The supermature quartzarenite of the upper Lorrain represents deposition in the turbulent shore zone. The Bruce, like the Gowganda Formation, may well be of glacial origin.