“What mystery pervades a well” is written in six stanzas of four lines each. It uses iambic tetrameter and trimeter: lines of four or three sets of iambs, or alternating unstressed and stressed syllables.

There is one notable variation in the length of the lines: “Where he is floorless” (Line 15), which stops abruptly at five syllables, ending on an unstressed syllable rather than a stressed one. The following line returns to iambic tetrameter. This deviation in rhythm causes an auditory break and draws the reader’s attention to the word “floorless” (Line 15). The drop in rhythm emulates the ocean’s vast, fathomless expanse as well as the unconquerable divide between the full breadth of nature and human knowledge.

The rhyme scheme is ABCB, with the second and fourth lines of each stanza rhyming. Many of these are perfect rhymes, such as “most” and “ghost” (Lines 18, 20). Others are near or slant rhymes, such as “glass” and “face” (Lines 6, 8). The poem uses clear, simple language, favoring monosyllabic words. There is only one word, “timidity” (Line 16) that has three syllables.