1. By determination of the internal pore space in blocks of soils and comparison with the observed value for the linear shrinkage it is found that a linear relationship appears to exist between the two values. 2. By extrapolating the curve thus obtained an approximation for the limiting value of the shrinkage in the case of pure colloidal clay is arrived at amounting to approximately 23 per cent. 3. On this assumption it becomes possible to calculate the approximate content of colloidal material in any soil from a knowledge of the linear shrinkage. 4. Results are adduced, showing the values obtained for the shrinkage in the case of separated fine silt and clay fractions in the case of two soils of known shrinkage and physical composition, and compared with the values calculated from previous assumptions. 5. The results of the calculation of the content of colloidal clay in the foregoing manner in the case of 16 Leeward Islands soils are appended.