THE HELICOPTER PILOT WAS ON AN AERIAL OBSERVATION FLIGHT & DESCENDED TO ABOUT 50 FT AGL TO SHOW HIS PASSENGER A MONITORING STATION. HE DID NOT SEE TRANSMISSION LINES AHEAD UNTIL A COLLISION WAS EMINENT. HE PULLED UP TO AVOID A SET OF TELEPHONE LINES & SAW POWER LINES DIRECTLY AHEAD. HE ATTEMPTED A QUICK STOP MANEUVER TO AVOID THE POWER LINES, BUT LOST CONTROL OF THE HELICOPTER. IT THEN STRUCK THE GROUND & ROLLED OVER.