Sec. 2. RESERVATION OF MINERALS AND MINERAL RIGHTS TO STATE FOR PERMANENT SCHOOL FUND. All minerals and mineral rights in, on and under said land are hereby reserved unto the State of Texas for the use and benefit of the Permanent School Fund, provided, however, that in the event of discovery of oil or gas in said land, drilling operations thereon shall be restricted so that not more than one well productive of oil or gas shall be drilled for each one hundred sixty (160) productive acres, and all operations at each such well shall be confined to an area or areas of four (4) acres at and including the well site.