by deposit of title deeds is a form of mortgage recognised by Section 58(f) of the TP Act, which provides that it may be effected in certain towns (including Calcutta) by a person ‘delivering to his creditor or his agent documents of title to immovable property with intent to create a security thereon’. That is to say, when the debtor deposits with the creditor the title deeds of his property with intent to create a security, the law implies a contract between the parties to create a mortgage, and no registered instrument is required under Section 59 as in other forms of mortgage. But if the parties choose to reduce the contract to writing, the implication is excluded by their express bargain, and the document will be the sole evidence of its terms. In such a case the deposit and the document both form integral parts of the transaction and are essential ingredients in the creation of the mortgage. As the deposit alone is not intended to create the charge and the document, which