I wrote this piece ten years ago, but have just made a new multitrack recording of the parts, so I thought I would share it here. Yes, you are correct. The bass line is being sung by an alto dropped down a well. (GarageBand makes it possible for me to sing all the parts, but I have to use the transpose feature to record the lowest bass notes, which creates a little distortion to the sound quality).
The sheep is a genius of place;
why would she stray?
Here is the homeland. Here, her mother's house.
Feed my sheep. Lead them home. Let them rest.
Sisters, all among the hills, chanting their Daily Office:
"There the rain licks into little pools. There, a dip to hide new lambs."
"Take my coat," she said. "You are a guest."