This note contains a brief account of the stratigraphy and mineralogy of the Cornish greenstones. Data obtained from ultrasonic, uniaxial compressive strength, Young's Modulus and wet and dry density tests are given for four greenstone types ranging from unmeta-morphosed to completely recrystallized contact-altered material. Differences in the results seem to reflect fairly closely the particular mineralogical and textural features of each sample. Commonly the greenstones are extremely tough rocks. Some of the implications of this fact are discussed with regard to site engineering problems, but more specifically with reference to past and present utilization and to the future potential greenstones could have as the raw material for engineering surface plates.