Observations have been made on the craters produced in plaster of Paris targets by steel pellets that weighed 2 g and impacted at a velocity of 2.5 km/sec and by aluminum pellets that weighed23 gand impacted at a velocity of 4.7 km/sec. The angle of impact was varied from normal incidence to 75°. For angles of incidence between 0° and 45°, the mouth of the crater was substantially circular. At 60°, it had roughly the shape of an arrowhead. At 75° obliquity, the pellet ricocheted and produced an elliptical crater.The area of the mouth of the crater in every case was many times the area of the impacting particle. The craters were characterized by a large bowl-shaped excavation from12in. to 1 in. in depth with a shaft that extended a few inches into the plaster and whose area was approximately that of the pellet.The volumes of the holes have been measured and related to the impacting energy and momenta of the respective pellets.