The Canadian Shield is mostly composed of granite, and patches of rock outcrop cover about 30% of the Shield. Soils on the outcrops are much shallower than forested areas and the vegetation communities that persist on the rock outcrops are not well known. This thesis explores the control of the physical factors on the soils and vegetation communities that develop on the rock outcrops (barrens) in the Thunder Bay area. In this thesis I investigate the relationship between parent material and soil chemistry characteristics, and the importance of physical factors in determining species assemblages. The research area was located in Thunder Bay, Ontario, along the north shore of Lake Superior and included five sites with different parent materials. The bedrock geology in the area is Archaean (granite) to Proterozoic (Gunflint Formation) in age. Soil samples were collected in the field and analyzed in the laboratory for: bulk density, moisture content, organic matter content, available nutrients, cation exchange capacity, particle size distribution, water holding capacity, and pH. Nonmetric multidimensional scaling was used to identify physical factors that control the variation in species assemblages and analysis of variance was used to test for differences in soil characteristics among the sites. Distinct vegetation communities were present at each site and the physical factors controlling vegetation structure differed among the sites. Generally the main controlling factors were exposure, pH, organic matter content and available nutrient concentrations. Significant differences in soil chemistry among the sites were reported that indicates the important role of lithology in soil development.