Samples of 15 rocks with porosity ranging from nearly zero to 40 percent were deformed under the constraint of uniaxial strain by stresses which reached 30 kb. No faults formed, although widespread small scale fracturing accompanied the compaction of the more porous rocks. Rocks with porosity less than 2 percent recovered from a cycle of loading with negligible permanent strain. Calcite twinned extensively in Bedford limestone and white marble, and in the latter there was indirect evidence of recoverable flow. Rocks loaded uniaxially reached very nearly the same stress-strain state as rocks loaded first hydrostatically and, then, in triaxial compression. The onset of dilatancy for granite, limestone and marble was close to the stress in a triaxial experiment at which strain was uniaxial.