Via Alan Lomax's facebook page:
http://roothogordie.wordpress.com/2012/09/24/alan-lomaxs-list-of-american-folk-songs-on-commercial-records/
Quote
Alan's 1940 "List of American Folk Songs on Commercial Records," compiled with the help of his sister Bess and a young Pete Seeger, was the culmination of many hours spent listening to an estimated 3000 pre-war hillbilly and race records. It's now available digitally as a PDF through the Root Hog Or Die blog run by ACE's Nathan Salsburg, who offers context for the list and its influence.
http://roothogordie.wordpress.com/2012/09/24/alan-lomaxs-list-of-american-folk-songs-on-commercial-records/