Final answer:
The poetic sound device is alliteration.
Step-by-step explanation:
The poetic sound device represented in the highlighted portion of William Blake's poem 'The Tyger' is Alliteration. Alliteration is the repetition of consonant sounds at the beginning of words in close proximity. In this case, the repetition of the 'd' sound in 'distant deeps' and 'distant deeps or' creates alliteration.
Learn more about Poetic sound devices in 'The Tyger' by William Blake