Here is a close-up of the hole which the coal would fall through (on the left - note the sloped sides). The metal insert had sloped sides to act as a funnel. The ground below (which can barely be seen through the hole on the right - which BTW, had nothing to do with the operation - someone just took the board away) was between 15 and 20 feet deep. This is the way we found the trestle - no wonder they are so concerned about people walking the tracks - what a nasty fall it would be to step in this hole!