Here's another one from Documenting the American South. There are some discussions about spirituals.

G. R. Wilson (Gold Refined)
"The Religion of the American Negro Slave: His Attitude Toward Life and Death"
From The Journal of Negro History, Vol. 8, 1923. p. 41-71.
Lancaster, Pa; Washington, D. C.: The Association for the Study of Negro Life and History, Inc., 1923.
Click here.