Submarine echoes of explosive sound are received which show abundant signal strength after traveling over 2000 miles total path from a 50-pound shot source; predominant frequencies are in a 5 to 50 cycle per second band. With certain basic assumptions, the reflector positions for the echoes are calculated. In every case but one, these positions correspond to known submarine structures with steep gradients. Most of the structures are the steep submarine slopes of the islands surrounding the northeastern Caribbean. Several seamounts to the east of Bermuda are reflectors. It is concluded that there is an uncharted seamount in the vicinity of 33° 22′ North Latitude, 60° 48′ West Longitude. Significant echoes are received from another seamount on which the least recorded sounding (probably not the actual peak) is 1270 fathoms Discovery of shoal areas and submarine structures can be greatly facilitated by the use of submarine echoes.