"at the cemetery, walnut grove plantation, South Carolina, 1989" by Lucille Clifton describes the unmarked graves of slaves who were responsible for building a majestic plantation in South Carolina, and asks why they were considered so unimportant that they were not even mentioned as people who helped to build the plantation on a tour she took of the property.
"Song" by Adrienne Rich discusses what loneliness is, but with irony she asserts—based on situations described—that loneliness may not match the definition the reader might attribute to the word. Additionally, the title of the poem may add some initial confusion to the reader.
The rhythm Clifton uses resembles a chant or a prayer. This is appropriate for the poem's theme of slaves who helped to build a plantation into a beautiful and successful "business" who were later placed in unmarked graves. The men were only listed on inventories as property, and the women were so poorly thought of, that they were not listed anywhere. The prayer is said over these dead whose lives mattered despite the fact that those people that "owned" them showed them no regard as human beings. The poem is written as if Clifton tries to put their spirits at rest and honor their existence.
The rhythm in "Song" is more syncopated, almost musical in nature; the poem's title is, after all, "Song." The author's definition of lonely is not what we might expect: she writes of a plane flying over the beautiful Rockies (mountains); of a woman driving cross-country who passes through towns where she chooses not to spend the rest of her life; of waking on a cold, beautiful morning while the contentment of others sleeping surrounds one with peace; and, of a rowboat that man be frozen in the ice, but knows it is not something passing or passive, but something that has the "gift of burning"—the ability to burn means the ability to give life. Fire has always been associated with life (i.e. Prometheus gives man fire), and the image does not bring with it an sense of loneliness, which is, I believe, the intent of all the examples provided in the poem. The main idea here may be that not all who are alone are lonely.