Brierley, J. A., Stonehouse, H. B. and Mermut, A. R. 2011. Vertisolic soils of Canada: Genesis, distribution, and classification. Can. J. Soil Sci. 91: 903–916. The Vertisolic soil order is the most recent addition to the Canadian System of Soil Classification (1998). Soils of the Vertisolic order in Canada occur within the Brown, Dark Brown, and Black soil zones, associated with the Prairie ecozone. Due to the absence of swelling clays in central Canada, morphological characteristics of Vertisolic or vertic intergrades are not recognized in soils occurring to the east of Manitoba. Finetextured parent materials dominated by the presence of swelling silicate clays in conjunction with appropriate climatic factors are the principal soil-forming factors for these soils. Two Great Groups are recognized within the Vertisolic order: the Vertisol and Humic Vertisol. Soils of the Vertisol great group are associated with the arid portions of the Prairie ecozone, specifically the Mixed Grassland ecoregion, and Brown soil zone. Humic Vertisols occur within the Dark Brown and drier portions of the Black soil zone. Each Vertisolic soil great group contains three subgroups: Orthic, Gleyed and Gleysolic. Classification to this level is based upon the presence of mottles (reflecting the duration of soil saturation) within the upper 50 cm of the surface. Vertisolic soils develop in finetextured parent materials of high shrink-swell potential and pose problems for agricultural land use and engineering purposes.