Using Werner Herzog's extraordinary documentary film, Cave of Forgotten Dreams, about the discovery of a cave full of Paleolithic art, three poets-Gale Batchelder, Susan Berger-Jones, and Judson Evans-decided to collaborate. Together and individually, they worked over time, with comments and revisions by the others, until the poems in Chalk Song began to take shape, the inimitable weaving together of three voices guided by sonic reverberations,...