As part of the study on land reclamation and consolidation for farmland in the tertiary type landslide area, the amount of slaking in the bedrocks of the tertiary type landslide was studied, in the light of the nature and physics of soil, in relation to the mechanical and physical characteristics of the bedrocks.The experimental results obtained with the rock samples were first interpreted and analyzed according to the existing theories;some of the phenomenon observed, however, were found not to be explained.<BR>In the present work, the amount of slaking was examined in conjunction with the shrinkage characteristic as well as the degree of soil structure development. The following are new insights gained in the present work:<BR>(I) Relation between Shrinkage Characteristic and Amount of Slaking<BR>Soft rocks undergo three types of shrinkages, i.e.normal, structural, and residual shrinkages;the development degree of each varies with each soft rock.When the degree of drying shrinkage per unit moisture content of a rock in a state of an undisturbed sample is expressed by the coefficient of shrinkage change (k), the following relation is obtained between the amount of slaking and the shrinkage.<BR>i) If k_max=0.3 to 0.5, normal shrinkage, or shrinkage closely related to it, occurs first and is followed by residual shrinkage.A soft rock with such a shrinkage characteristic has a large amount of slaking (group A and B in Table 4).<BR>ii) If structural shrinkage continues until a fairly low moisture point and residual shrinkage that follows has k_max nearly equal to or less than 1, the amount of slaking is small (group C in Table 4).<BR>iii) If k_max has an intermediate value between the above two, the amount of slaking is also between those of i) and 11).<BR>(II) Relation between Soil Structure and Shrinkage Characteristic<BR>If R, a parameter indicating the degree of the structural development of soil, is large enongh, structural shrinkage takes place, followed by a shrinkage process whose characteristics are given in the following:<BR>i) Normal shrinkage, or shrinkage closely related to it, occurs followed by residual shrinkage.This applies to rocks belonging to group A in (I) i).<BR>ii) Residual shrinkage takes place to a small extent;this applies to rocks of group C in (I) ii).<BR>If R is small (R=1 to 2), practically no structural shrinkage is observed, and normal and residual shrinkages start immediately.This applies to rocks of group B in (I) i).<BR>The above correlation between the rock characteristics and the amount of slaking led the author to propose classification of rocks and soils for various soft rocks.Interpretation of slaking from the angle of soil physics is as follows: if the degree of drying shrinkage per unit moisture content is large that is, if soil grains greatly changes their positions relative to one another, the corresponding soft rock will bave a large amount of slaking: under such dried conditions, silica acid gel films inaccessible to water molecules tend to crack and cause slaking.