Daniel Snow is a waller, an artisan who builds walls, terraces, caverns, and the occasional sphere or pool out of dry stone. It's an ancient skill--building with only what the earth provides. No mortar, no nails, nothing to hold his creations together except gravity, an invisible glue he can sense in the stones' "conversations" of squeaks and rumbles. A hollow sound means a void needs to be filled; a solid fit is secured with the sound of a bolt being thrown. Snow's evocative prose and Peter Mauss's richly textured photographs of Snow's work reveal the nuance and beauty of walling--and of one man's relationship with nature. The result is by turns poetic and practical. (