Twelve soil profiles, developed on gravelly parent material, have been sampled in the region of Quebec City and analyzed. Six profiles are developed on sandstones and shales whilst the six other profiles are formed on shales and mudstones. The shales, and to a lesser extent the sandstones, weathered readily to produce a large percentage of clay. Because of this, many B horizons with significant pyrophosphate-extractable Fe and Al do not meet the criteria for a Podzol B. The coarser than 2 mm material, which ranges in individual horizons from 14 to 82% in the first group of soils and from 0 to 84% in the second group, cannot be ignored as it contributes up to 69% of the total exchange capacity of the soil and therefore is important for the natural fertility of the soils. The differences between the stability of the gravel in air and in water also explain some of the problems in classifying these soils.
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Rivard et al. (1980) studied this question.