Encore Puzzler - 9/12/98: Trees and Mines

RAY: Some years ago, my wife and I took a trip south, down the east coast, from our fair city of Boston. I forget what our destination was.

TOM: But it was all down hill.

RAY: Right. I forget what our final destination was, but somewhere around West Virginia I got the notion that I wanted to explore some abandoned mines. I engaged a guide named 'Lefty...'

TOM: Formerly an Everglades tour guide.

RAY: Right, but since that fateful swim with a 'gator, he could no longer operate the controls of the tour boats. So he takes me through a few. Now, my only recollection of mines was from the old westerns, where the roof and walls were shored up with timbers.

TOM: Like Volvo does.

RAY: I was surprised to find that in fact they still do that. I asked Lefty what kind of wood they used, because I didn't recognize it. He said "I only know 'gators, not trees." To my surprise, all the other mines used the same wood. I would have expected them to use Oak or Ash, strong woods plentiful in the area. But it turned out to be Tulip Poplar, which I thought couldn't possibly be near as strong as the aforementioned trees.

Question: Why was this the only kind of wood used to shore up these mines? Hint: It had nothing to do with the trees' proximity to the mines.

[ Car Talk Puzzler ]