AbstractIn both Catalina clay and Cialitos clay there are no marked differences in the properties of the different-sized aggregates and the corresponding whole soils studied. Although well-drained upland soils in the Tropics are supposed to contain less organic matter than those in the cooler Temperate Zones, the organic-matter content of Catalina clay and Cialitos clay was as great as that found in many soils of the same texture in Temperate Zones. Organic matter has a very definite influence as a cementing agent between clay particles. This was shown by the low clay values obtained when or ganic matter was not removed by pretreating the soil with hydrogen per oxide prior to mechanical analysis. From the general data obtained in the study of the aggregates of both soils, it can be inferred that they are formed largely as a result of the breakdown of large massive units of soils. If synthesis occurred to a larger extent, more marked differences could be expected in their constitutional makeup.
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