A colleague interested in iron mines in Putnam County, New York, active in
the 18th and 19th centuries has discovered stone blocks with inscribed
names at one site. These blocks contain drilled holes that are round at
their bottoms. He has heard that this is diagnostic of the date of
drilling, since the time when miners changed from using drills with rounded
points to those with flat points (as in a modern star drill) is well
known. Can anyone confirm this, and tell us the date of the change?
Robert Gordon
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