Monson Maine Slate Company, ca.1900
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This is an open pit slate mining operation showing the men going down into the quarry in the "box" which was lowered into the pit by the hoist shown on the upper right of the photo. The slate would then be brought up to the top of the quarry by the chains used to lower the "box".
There were a series of bells used to tell the hoister operator if the men needed to come up to the surface, if a load of slate was ready to be raised, and so on. The series of indentions shown in the photo were called ledges.