When Boston started getting skyscrapers

On DesignerBlog, Will begins a series on construction of the Pru and the Hancock:

... The excavation site became a major attraction. People lined the fence and waited eagerly to see how far down each pile would go. Anticipation increased after a hundred feet, then a hundred and fifty; a hundred and seventy five. Finally, at one hundred and eighty feet, the first pile bounced back up about a foot. It was struck again, and bounced again. Very gently it was tapped into place against solid rock. Now they knew. ...