Provided alwaies and be it enacted by the Authority aforesaid That no Boat or Barge belonging to the Towne of Knottingley or any other Towne or Place scituate lying or being on the Banks of the River Aire between the said Towne of Knottingley and the Place where the Aire falls into the River Ouze laden with Lime only shall be subject or lyable to any Duty for passing through any Locks or Weares to be erected by the Authority of this. Act below Knottingley Mill Dam scituate upon the said River of Aire to which Place the said River is navigable.