U.S. Geological Survey Open-File Report 03-221
A Pictorial Survey of the Bedrock Beneath Western Cape
Cod, Massachusetts
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Photograph shows the sonic drill rig with the drill casing almost completely penetrated. The sonic rig also utilizes a dual line of drill pipe. The inner string of drill rods has the core barrel attached. All overburden core sampling is done ahead of the outer string of drill casing. After the core barrel has been advanced, the outer drill casing is advanced to the same depth. With the outer casing left in place to hold the hole open, the core barrel is then removed from the borehole.
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