There are lots of good collections of Bill Monroe’s music out there, but if you want to get down to the deep roots of the early bluegrass sound, this is the place to start. Consisting of recordings made between 1945 and 1949 for the Columbia label, it includes early versions of most of his most famous songs, including “Why Did You Wander?” (taken at a breakneck pace), the tear-jerking “Footprints in the Snow,” and “Mansions for Me,” a gospel tune that harks back to his time working as a duo with his brother Charlie. The sound is surprisingly good.