Yule marble has been experimentally deformed at 150°C under conditions otherwise identical with those at room temperature reported in Part I. The strength is lowered about 40 per cent by this increase in temperature, and the relative ease of translation versus twinning on is increased. Fabric measurements on the deformed material show trends nearly identical with those at room temperature (Part III). The individual grains are more homogeneously deformed, and, perhaps as a consequence, the fabric changes appear to be somewhat more sharply defined. Effects of interstitial water and of slow rate of deformation are negligible except for a lowering of strength similar to that observed at room temperature. The fabric changes are completely consistent with those predicted in Part II under the hypothesis of homogeneous deformation. By all tests applied, the mechanism of deformation is thus the same as at room temperature, and is dominantly twinning and translation on . The observed lowering in strength and greater homogeneity of texture suggest an approach to conditions of natural deformation.