This photo shows tunneling under Central Park for the Lenox Line. Unlike cut and cover, these tunnels are deep underground and cannot be built by digging through the street. Drillers made holes for dynamite that helped explode the rock, and then excavators removed the spoil and cleared the way for the shield, a device that kept workers safe as they dug. The shield is a temporary support that acts to protect the workers from falling debris as they chip away at rocks ahead of the shield and put in place permanent support walls behind it. Sandhogs used pickaxes, shovels, air powered drills, and sometimes dynamite, to break through the rock.