Robert,
I believe the song is "Rock of Ages", an OLD spiritual that is still sung even today. If you ever watch "Little House on the Prairie", it seemed like every time they did a church scene they would sing that song. Below is a link to some of the history of the song.
http://www.faithalone.org/journal/1995ii/Mosher.htm
Respectfully,
Gerald D. Hodge, Jr.
War Between the States Historian
Historian: 39th Georgia Volunteer Infantry Regiment
http://39thGAVOLINFRGT.homestead.com/39thHomepage.html