the next layer of mineral above the salt is shale. It is very hard and brittle and constantly breaks off in pieces whenever they blast. The percussion underground from these faces when blasted is incredible. Areas with only shale on the ceiling are a constant hazard because there are always "loose" pieces waiting to fall from the ceiling. The salt is a soft rock and still strong at the same time. It has much more "give" to it. When I alluded to older areas of the mine that had "caved-in", it was due to the fact that there was not a layer of salt left on the ceiling in that area. Over time, the shale and subsequent layers of earth broke free and collapsed from the daily blasting. A few years back we had to change the time of day of our blasting schedule. We would literally wake people up in the night in their homes and it wasn't uncommon for pictures to be knocked off walls and such. If standing on ground above an area to be blasted, you could feel the earth tremble below you. I have felt it as far as three miles away in my fathers back yard. No lie !! Have a great one today Kelley,
Rob