Sociologist w. e.b. du bois observed that a dual heritage creates conflict for people of color: an identity conflict of being black and american. du bois referred to this duality as

double-consciousness

Explanation:

The concept of Double consciousness was first described by the Sociologist W.E.B. Du Bois, in his book "The Souls of Black Folk" in 1903. Doubles consciousness refers to the double social identity which makes it difficult for them to develop a sense of self. He studied this concept concerning the racial identity prevailed in the United States of America. It refers to the difficulty of the African Americans to develop a sense of American identity with their Black identity.

permafrost layer, it exists beneath a layer of soil, rock or sediment.