Show BURNING COAL BEDS FORM NATURAL BRICK many coal beds in the great coal fields of the western stites have at 1 some time taken fire and barnd along their out baking and re i dening the oveil ving strati strat so that they ha have become a kind of natural brick or terra term cotta tho the fires in placed hot enough to fuse and re crystallize the overlying shale and sandstone so as to form nathal slag at some places the slag rt true igneous rock at others it consists largely of rare minerals thoroughly fused slag seems to occur chiefly in crevices or chimneys through which the hot gases generated in the burning escaped through the strati strat to the suffice sur surf fice ice the chimney shaped masses of slag lag are harder than the surrounding baked rock and after that has wreathed awa form the curious pin acles that surmount man clinker bluffs or buttes in the west some of tho tha coal beds those exposed on the higher hills w were e ter perhaps laps ignited bv bi lightning others according to well authentic bated rev reports orts were ignited by branie fires or camp ores but as burning on the outcrop has been so common as to effect most of the coal beds in an irei trea of more than square miles much of it has probably been due to spontaneous combustion coal beds are now burning at or neat the surface at man places in the west where the burning of the bed is disclosed by the smoke and f fumea umes that arise from it and bv the heat at the surface of the earth near the outcrop or above the bed heat so intense that it kills all vegetation As the coal burns out the rock or earth generally can caves es in so 0 o as to form I hryc irge tissues in the ground As aitho tho burning oils back from the outcrop the heat acts on the overlying rocks but finall combustion is smothered for the lack of oxygen it is difficult to sa sav how far barbick inck from front tre outcrop the burning maj ma c attend field studies made by the united states ecological geological 6 sur burvy y department of the anterio in terio indicate that a bed 13 bing ing bene beneath etli 20 feet or less of co cover er may buu buc bu u c out 13 under large greas and even cen where the cover is hundred feet thick the burning mav ma extend feet back from front the outcrop A brief account by G S rogers of the burning of coil beds it in place with a discussion of the cau causes ps and a petrologic ind chemical description ot some of the baked aud fused rock formed has been published by the united states geological sersey as professional paper A A copy of thid this report ma mav be obtained freo on cn application to the direktor dt di reitor of the sur survey ey |