No one has mentioned the collection, "Slave Songs of the United States" collected by William Francis Allen, Charles Pickard Ware, and Lucy McKim Garrison, from 1867--it was the place that first introduced songs like "Follow the Drinking Gourd","Run, Nigger, Run!" "Michael Row the Boat Ashore" Roll, Jordan, Roll"(and many others) to the wider world--
Dover has reprinted the original version, with a preface by Harold Courlander, and it is inexpensive and wonderful..
A slave song that I have always loved, both for it's story and for the song itself, is "This May Be the Last Time", which, it is said, was traditionally that last song sung by slaves who met when their masters got together, and alluded to the possibility that the group might never meet again, because of the possibility of being sold, or worse--
"Time for Us to Go" scans perfectly to the melody of "Log Jam on Gerry's Rocks"--
This is a very interesting thread--I guess because it touches on a sensitive point, and that is that our culture's music has been fundamentally shaped by a group people who have(and continue) been horribly abused and mistreated by the culture--