Travelling through the islands part 3 The concession area was one of the most daunting that any geophysical crew could be faced with, as the surface geology was basalt rock that had been volcanically erupted thousands of years ago, covered with a layer of primary jungle. The basalt ridges rose to two or three hundred feet high at a maximum interval of five hundred foot separation and the top of each ridge was razor sharp so it was like traversing a giant set of piranha teeth that had never been flossed. To lay a recording cable and geophones in a straight line over this natural land barrier required a five hundred strong team of front cutters armed with machetes and five hundred strong back crew making ladders and bridges from bamboo and laying the cable. It sounds difficult dealing with that number of people but they employed a system of headmen who ran their own hundred strong crews on a sub contract basis so the company representative only ever dealt with ten headmen at most. Once geophone array had been deployed a pattern of dynamite charges was set off and the speed of the returning shock wave recorded electronically. After interpretation, the speed of the returning signal determines the nature of the area sub surface geology and where basement is, it also revels any formations or salt domes that potentially contain pockets of oil or gas. Having started the line had to be completed due to security precautions as leaving pre loaded holes with detonators and one kilo sticks of blasting dynamite lying around is not permissible. This meant the recording and survey crews remaining in the jungle on a semi permanent basis housed on recording platforms constructed by the cutters and porters. These platforms also served as drop zones for the Bell bubble helicopter which was flown by an American fresh out of Vietnam but nobody had told him the war was over as he insisted on making strategic approaches to the DZ to avoid incoming. A very dangerous practice with two sacks of rice hanging on the skids. The work done by this crew got a write up in the National Geographical magazine for record production of five kilometers in one month a world record at the time and probably not much different today in that inhospitable terrain. For comparison a desert seismic crew average three hundred kilometers a month but then again barring sand storms nature is on your side.