This document discusses several types of excavation machinery: power shovels, draglines, clam shells, backhoes, and trenching machines. Power shovels excavate earth and load trucks, and can be mounted on tracks or wheels. Draglines are useful for long reaches and underwater excavation. Clam shells remove materials from vertical excavations. Backhoes have an articulated arm with a digging bucket. Trenchers dig trenches, especially for installing pipes or cables.