Just over a decade ago Canada's top geologists sat down to review progress over the past 110 years. They found, despite rugged efforts by generations of tough, hard-bitten predecessors (the Geological Survey of Canada has operated since 1842) more than two-thirds of Canada's sprawling 4,000,000 sq. miles were still unmapped geologically. For a nation so dependent on mineral wealth it was a vital situation. At this rate, another century and a half was needed to finish even a preliminary survey of the country. It was then the helicopter came clattering with whirling blades into the geological picture, to provide a far-seeing observation platform. Combined in operations with fixed-wing airplanes, the helicopter became a magic carpet from which the skilled scientific eyes of experienced geologists could range over mountains and valleys, lakes and barrens. Today, the Geological Survey of Canada launches nearly a dozen simultaneous airborne operations a year. Helicopters, float-planes and balloon-tired aircraft carry geologists on scientific surveys that would have taken scores of years by previous pack-horse, canoe and dog-sled methods. Yet, though this airborne assault is expected to complete the reconnaissance mapping of Canada by 1970, there is still lots of old-fashioned foot-slogging to be done. In fact, during a single field season, some airborne party members may walk more than 500 miles and climb enough mountainsides to total five times the height of Mount Everest.