TWO CAT LOADERS WERE IN A #4A COAL PIT AT THE MEAD/ZINN NORTH PIT OF THE BOWMAN STRIP OPERATION LOADING COAL. IT HAD RAINED HARD THE NIGHT BEFORE AND HAD RAINED EARLIER IN THIS SHIFT. A SECTIO N OF THE HIGHWALL FELL AND HIT ONE OF THE LOADERS BELOW, THE ROCK HIT MAINLY THE LEGFT SIDE AND FRONT OF THE LOADER--SOME OF THE ROCK CAME THROUGH THE FRONT WINDESHIELD, HITTING THE OPERATOR.