''I don't see why,'' he said, dallying talk while hooked on a crossword's puzzling spaces, ''why a wall needs cleaning. Do tree-trunks?'' and could have added stones, beetles' backs, toads, flies, all that's out of doors in rain/wind/sun. I've cleaned our wall for summer years and have my reasons why. It's recognized that rocks settle, can split and fall, shift- ing with spring's thaw. A wall moves in glossed time, each part fitted in a slow-changing grip. I start at the left of the steps, my tools an icepick and trowel. Winter's skeletal leaves and brittle sticks lie bedded in cracks, dank holes enlarged by chipmunks, fickle caves. I lift a layer, crackle-dry on top, held with the glue of moisture so I see the shape of maple and ash as I turn it like a pancake, then plate it amongst sweet-fern already a foot high. In this crevice cherry seedlings have taken hold. A glistening adhesive trails the retarded snail, darkly sealed. I let him be. And here, ah, with vigorous strength I firmly pull the lengthy root of a dandelion. It all repeats. A ruffled mat of brown debris follows me as, slapping gnats, I work my satisfying line. Tomorrow I will clean the other side.