The supervising board or any person authorized by it in writing, may, during business hours, in the presence of the treasurer or his deputy or clerk, inspect and examine the books of account in the office of its treasurer and all contracts, writings, securities and other papers belonging to the depositing unit or pertaining to the business thereof, held by the treasurer, and may inspect and count the moneys belonging to the county and the several funds thereof in the custody of the treasurer; and it is hereby made the duty of the treasurer to furnish all reasonable facilities for the purpose.