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Diagrammatic horizon patterns for five typical subgroups of these soils are shown inFigure 5.The principal unit of classification is the soil series, which may be subdivided into soilphases, based on differences in the texture of the surface horizon . Each soil series is defined interms of the kind and texture of the parent material, and the characteristics of the soil horizons .The soils occurring within the limits of a soil series must have similar horizon development . Sincesoil is a three-dimensional continuum, the features of each horizon vary both laterally and vertically.The principal soils occurring in the region are named and described in this report, but minorsoils of limited occurrence may not be discussed . The profile descriptions in the Appendix, presenta central concept of each principal soil . The name given to a soil is usually a geographical name,referring to an area where it was first established, e.g., New Liskeard soil, a name given to a soilfirst mapped in the New Liskeard area .Soil Map UnitsDifferent soils may occur in such close proximity in a landscape, that they cannot beseparated at a particular scale of mapping. Complex map units are established, which recognizethis fact . Map units are named after the dominant soils which are present . Simple map units occurwhere one soil is dominant, and there are only minor inclusions of other soils . Complex map units,on the other hand, occur where two or more soils are present in significant amounts in thelandscape, but which cannot be separated at that mapping scale . These map units may also containminor inclusions of other soils, as well . Most map units in the Precambrian shield regions ofOntario are of this second type, consisting of the principal soil series plus, in many cases, rockoutcrop .It is usual practice to expect at least 20 percent of unnamed inclusions in any map unit .There may be instances where the proportions of unnamed inclusions exceed the 20 percent level,particularly in areas of poor accessibility . . .Soil PhasesA soil phase is a unit of soil outside the system of soil taxonomy. It is a functional unit thatmay be used to recognize and to name soil and landscape properties that are not used as criteriain soil taxonomy, e.g., stony phase, but which are important in land management.In Table 5, the drainage conditions of the soils, that are ma ; -red in the Ville-Marie mapsheet area, are indicated . Soils are listed alphabetically in the same line with similar soils that occuron the same parent materials, but have different drainage conditions .