INTRODUCTION Field geology provides a wealth of evidence relating to the kinematics of rock deformation. However, the origin of tectonic forces is conjectural; the state of stress in the crust can seldom be determined quantitatively, and the processes of slow deformations are never subject to direct observation in nature. The dynamics of rock deformation must be learned through controlled experiments which realistically simulate the natural environmental conditions—overburden and interstitial pressures, temperature, and time. This section outlines the results of these experiments, but includes neither the atmospheric-pressure engineering data, adequately compiled elsewhere [48, 89, 165, 166], nor a complete tabulation of the high-pressure properties of metals, which is thoroughly treated by Bridgman [30], EXPERIMENTAL METHOD AND DEFINITION OF TERMS In the laboratory the behavior of small samples of real rocks at high pressures and temperatures is investigated in the triaxial compression test. The cylindrical specimen with a diameter of about 1–3 cm is encased by the thin, impermeable, rubber or copper jacket and first subjected to the constant external fluid (hydrostatic) confining pressure, pc (Fig. 11-1). The ratio of length to diameter is 2 to 3, large enough to minimize the influence of end constraint, but small enough to avoid buckling. A measured quantity of interstitial liquid is injected by the volumeter through the hollow piston into the previously evacuated sample. The internal pore pressure, pv, is then raised to the desired value by thrust on the volumeter piston. The differential pressure,δσ, is applied by a hydraulic or