Wegener also noted that the continents move up and down to maintain equilibrium in a process called isostasy. As an example he cited the sinking of Northern Hemisphere lands under the weight of continental ice sheets in the last ice age, and their rise since the ice melted some 10,000 years ago.
Drill bits are cutting tools used to create cylindrical holes, almost always of circular cross-section. Drill bits come in many sizes and have many uses. Bits are usually connected to a mechanism, often simply referred to as a drill, which rotates them and provides torque and axial force to create the hole.
This website is not affiliated with the U.S. government or military. Drill Formations. Many drill procedures used by the United States Army today were developed during the Revolutionary War. The purpose of the drill then was to instill discipline in American soldiers. As these soldiers mastered the art of the drill, they began to work as a team and to develop a sense of pride in themselves and in their unit.