The Scouts were fascinated by the story that after 20 years, the miners had only recovered 10 ounces of gold (then priced as $20 an ounce).  After they found the airshaft they went another 20 years, and still only found 10 more ounces of gold.  That seemed like a LOT of work for such a little return, half of which had to be shared with the investors in the mine.