definition from Merriam Webster (http://www.merriam-webster.com/dictionary/glen)
From Beloved by Toni Morrison (page 95)
“When the busy day is done
And my weary little one
Rocketh gently to and fro;
When the night winds softly blow,
And the crickets in the glen
Chirp and chirp and chirp again; …”
Amy was singing her mother’s song. The lyrics describe a night when winds softly blow and the crickets in the small valley chirp.