Of all the seminal albums to come out in 1991-the year of Nevermind, Loveless, Ten, and Out of Time, among others-none were quieter, both in volume and influence, than Spiderland, and no band more mysterious than Slint. Few single albums can lay claim to sparking an entire genre, but Spiderland-all six songs of it-laid the foundation for post rock in the 1990s. Yet for so much obvious influence, both the band and the album remain something of a...