Adverbs are Formed from …
Parts of speech are also used as or made into adverbs.
(a) Nouns - Inside, outside, home-made, skin-deep, sea-borne.
(b) Adjectives - Pretty good. He works hard.
(c) Pronouns - None the worse. All the better.
(d) Prepositions - You go before, I will come after. I think he will pull through.
Note: To tell when a preposition is used as an adverb see whether it is followed by a noun. If not, it must be parsed as an adverb.
A cloth must be put underneath (adverb).
A cloth must be put underneath the books (preposition).