Step-by-step explanation:
Remember, a metaphor is a figure of speech that makes a comparison between two things that not related as though they are in other to give a description. We can infer from those words that the author has a negative view of the impact of slavery on human society.
The metaphor "blanket of ignorance" depicts a situation just as when one covers a "blanket of cotton" to prevent the body from exposure; similarly the "blanket of ignorance" has covered the minds of individuals from reaching their full potential. In a sense, ignorance has now become the order of the day after "three hundred years of slavery."