Abstract: The obtaining of undisturbed core samples of subsurface soils for analysis and study is disclosed. Percussion-type downhole drilling equipment uses compressed air directed internally of a pipe casing to actuate a percussion-type piston adjacent the bottom of a hole being drilled. A tubular adapter is mounted in a chuck at the lower end of a casing and house the piston and the adapter for rotation and for longitudinal movement relatively thereto. The adapter has a striking face interfacing with the piston and has its opposite end provided with pipe threads for connection of an open-ended core sampler which is preferably of the split-spoon type. The adapter is provided with ports at a location spaced axially away from the core sampler for exhaust air released by the percussion means during a power stroke upwardly and thus away from the core sampler.