Final answer:
In the text 'Sound of Thunder', I found a metaphor that compares a purple cloud-bank to the darkening lower edge of the setting sun.
Step-by-step explanation:
A metaphor is a figure of speech that compares two different things by stating that one thing is another thing. In the text 'Sound of Thunder', I found one metaphor:
'The purple cloud-bank darkened the lower edge of the setting sun, crept up and up, obscuring its fiery red heart, and finally passed over the last ruddy crescent of its upper rim.'
In this metaphor, the purple cloud-bank is compared to a darkening lower edge of the setting sun, creating a vivid visual image in the reader's mind.