§ 315. Recording books. Different sets of books must be provided by the recording officer of each county, for the recording of deeds and mortgages; in one of which sets he must record all conveyances and other instruments absolute in their terms, which are not intended as mortgages or securities in the nature of mortgages, and all executory contracts for the sale, purchase or exchange of real property, or memoranda thereof, and all instruments canceling or extending such contracts, which conveyances, contracts or instruments are delivered to him, pursuant to law, to be so recorded, and all forms pertaining to commitments of land to continued agricultural production required to be so recorded pursuant to section three hundred six of the agriculture and markets law; and in the other set, such mortgages and securities, and assignments of rent, delivered to him; excepting that if the recording is by microphotography or other photographic process, the recording officer shall not be required to maintain books for such records, but shall provide such filing equipment as he may deem appropriate. The recording officer may, in his discretion, record in consecutive order the instruments received by him, and shall not be required to segregate mortgages from deeds or other classes of instruments.