The controlling idea of a paragraph is its

answer: metaphor: because there is a comparison between the treasures spread on the ground and the evil seed of adam drifting from the shoreline  

explanation:

many is the pronoun that is used in this sentence. many is a quantifier that determines the amount of discoveries. when we use quatifiers followed by nouns, they act as determiners, but when they are used without a noun, as it is this case, they are pronouns.