What is one example of a symbol or metaphor in "The Lives of the Heart"?

Many readers may initially find the poem overwhelming
because of the swiftness and range of the symbolism, similes, and metaphors. Line 14,
for only one example, takes a rapid journey that might leave readers breathless to catch
up: “Rise up as cities, as serpentined magma, as maples.” Readers will need to supply
ideas about why the lives of the heart may bring people together in large cities.
Similarly, to compare the lives of the heart with magma suggests that there are
incredibly powerful forces at work within individuals, which at times may erupt, just as
a volcano erupts. But one of the end results of such eruptions is serpentined rock,
which may serve ultimately as the basis of sculpture, and more broadly, of art--this can
be a stretch for readers to see. “Maples” suggests the harvesting and manufacture of
syrup, which brings out the idea of sweetness, and of constructive thought. It may take
readers a little time to follow such a line, which is typical of the depth of mind
exhibited by Hirshfield. She does not invite passivity from her readers, but active and
engaged involvement.