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 that is fitted with a Pipe provides effective connection to the rig surface equipment or application with the bit and the bottom hole assembly for the purpose of pumping the Drill fluid to the bit.
When drilling glass base grades, a carbide drill should be used. The materials can be drilled dry with the aid of an adequate exhaust system. A flood of water soluble coolant on the work and drill can be used when necessary to prevent overheating and dulling of drills.