Here's the clickable link: http://www.traditionalmusic.co.uk/negro/
"On The Trail Of Negro Folk-Songs-online book
A collection of negro folk songs with lyrics, sheet music & commentaries.
By Dorothy Scarborough Assisted By Ola Lee Quiledge Copyright, 1925 By Harvard University Press "

This looks like an amazing resource. Likely somebody here has already pointed it out, but I've not seen it before. Amazing to see it all online
There are also good links with instrumental, vocal, and educational resources.

Here's the table of contents.
I. ON THE TRAIL OF NEGRO FOLK-SONGS.....       3
II. THE NEGRO'S PART IN TRANSMITTING THE TRA­DITIONAL SONGS AND BALLADS.........      33
III.   NEGRO BALLADS..................      63
IV.   DANCE-SONGS, OR "REELS''............      96
V. CHILDREN'S GAME-SONGS.............    128
VI LULLABIES......................    144
VII. SONGS ABOUT ANIMALS..............    161
VIII. WORK-SONGS....................    206
IX. RAILROAD SONGS..................    238
X. BLUES........................    264