00:31 Jan 20, 2011 

Yes, a noun is needed here, but for the sake of clarity, deposition is also a noun and in addition to meaning 'the act of depositing', it is a synonim for 'deposit', pls. see here: http://www.thefreedictionary.com/deposition Thesaurus Legend: Synonyms Related Words Antonyms Noun 1. deposition - the natural process of laying down a deposit of something
deposit
Pls. note that synonyms are marked with a vertical green line as shown in the Legend.
http://www.yourdictionary.com/deposition
depo·si·tion (dep′ə zis̸h′ən, dē′pə-)
noun
4. something deposited or left lying
Therefore, both are correct and have already been proposed within my answer and the peer comment to it entered by Katarina Delic; moreover, both are equally used in medical texts - this can easily be proven by simple google search, there are numerous examples, e.g.: http://books.google.com/books?id=5EWXxLthJ2YC&pg=PA730&lpg=P... In addition, hemosiderin depositions in the poste...