I wonder what those other cities are built on. The Second Ave subway's bedrock is schist [1] -- which is an extremely strong, durable type of rock. A quick gla

I wonder what those other cities are built on. The Second Ave subway's bedrock is schist [1] -- which is an extremely strong, durable type of rock. A quick glance at this [2] engineering book indicates Copenhagen is limestone. Apparently the same is true for Paris. Any engineers here who want to chime in about how that affects cost? [1] http://mobile.nytimes.com/2012/08/05/magazine/tunneling-below-second-avenue.html http://mobile.nytimes.com/2012/08/05/magazine/tunneling-belo... [2] https://books.google.com/books?id=6UAqS62NJDMC&pg=PA2616&lpg=PA2616&dq=copenhagen+bedrock+schist&source=bl&ots=hUa0ZXOwsc&sig=TcnFzKgNZRIw0pC6DLkp9PHokJA&hl=en&sa=X&ved=0ahUKEwjuu6KEuKLRAhXF7SYKHbg8AX0Q6AEITzAL#v=onepage&q=copenhagen%20bedrock%20schist&f=false https://books.google.com/books?id=6UAqS62NJDMC&pg=PA2616&lpg...