64 Pa. Stat. § 263
From and after the issuing of said warrant, the right to dig and mine for iron, coal, limestone, sand and gravel, fire-clay, and other minerals, shall vest and be in the party in whose favor the said warrant or warrants shall issue, his heirs or assigns: Provided, That he or they shall so exercise the said right as not in any way to interfere with the free navigation of said river, or with the rights of any person or persons holding property on the banks thereof: Provided also, That nothing contained in this act shall authorize any person to undermine the bed of any river, the navigation of which has been improved by the commonwealth or by any incorporated company, within one hundred yards from any dam, lock or other building necessary to said improvement, without the consent of the canal commissioners, or the board of managers of said company; and nothing contained in this proviso shall in any way be construed to extend to any works or mines now in operation, or to affect any rights now vested under existing laws: And provided also, That the commonwealth shall have the right, after twenty years from this date, to revoke any such warrant or grant, on payment to the party, his heirs or assigns, holding the same, the original purchase money, and the original costs of his works, engine, etc.; such power of revocation only to be in force where there is any improvement made.
64 P.S. § 263