Three very large quarry explosions of between 50 and 100 tons of high explosive in the Snowy Mountains area were recorded by seismographs at distances up to 375 km. P and S wave velocities within the Earth's crust for this part of south-eastern Australia were formally determined to be 6�04 (�0'04) and 3�62 (�0�03) km/sec, respectively. The P n velocity was found to be 8� 03 km/sec, with an estimated error of O� 2 km/sec. Assuming a uniform layer above the Mohorovicic discontinuity with these velocities, the discontinuity was formally estimated to be at a depth of 37 km.