The county surveyor or his deputy, in the performance of his official duties, shall have the power to summon and compel the attendance of witnesses before him, to testify respecting the location and identification of any line or corner. When any such witness testifies to any material fact, his testimony must be reduced to writing and subscribed by him and made a matter of record. The county surveyor and his deputy are hereby authorized and empowered to administer oaths and affirmations to any person appearing as a witness before them. But the testimony as provided for herein shall never be used as evidence in any action involving corners or boundary lines, except for the purpose of impeachment. Each witness shall be entitled to the same fees allowed in county court.