Symbolism, Imagery, Allegory
Thoreau is inspired by… mud. Yes, mud. The sight of this humble substance thawing initiates Thoreau's reflections on the interconnectedness of everything in life, from the muckiest mud to the most sublime ideas. As it thaws, the mud makes a distinctive web pattern that reminds Thoreau of leaves, which, in turn, makes him think about how certain distinctive patterns recur in nature. For Thoreau, this recurring pattern is nothing less than "living poetry":
The earth is not a mere fragment of dead history, stratum upon stratum like the leaves of a book, to be studied by geologists and antiquaries chiefly, but living poetry like the leaves of a tree. (Spring.9)
The sight of this pattern confirms Thoreau's belief that natural beauty corresponds to human spiritual truths.