The motives of the two men engaged in the enterprise were not exactly similar. David, according to what he told Leighton, hoped to solve an archæological riddle and to study a hitherto lost people whose prehistoric civilization equaled that of their neighbors, the Incas of Peru. Arthur, on the contrary, whose fortune was still to be made, regarded it frankly as a mining scheme that promised fabulous returns in money, with a comparatively small amount of risk and labor. The two points of view were not antagonistic, and for a time the friends worked amicably enough together. In Bogota they easily secured from the government the necessary permit to drain Guatavita. But the attractions of the Colombian capital, the hospitality with which they were received, delayed the actual working out of their plans. Fascinated by the romance of this picturesque city and charmed by the unique race of mountaineers inhabiting it, David postponed the prosaic task of mining, while Raoul became absorbed in studies relating to their proposed venture, meeting people with whom his companion seldom came in contact. Lake Guatavita and its secret was thus, for a time, forgotten--at least by David. When the social gayeties of the capital were exhausted, he took up in earnest the work he had planned to do. He bought a full equipment of the best mining machinery and hired a large number of laborers. But the enterprise proved more difficult than he expected. The Spaniards, who had worked at the problem three centuries before, were bound to fail on account of their lack of engineering machinery. To empty Lake Guatavita, they tried to cut through the mountain which formed one of the containing walls of that body of water. Under the circumstances their partial success was amazing. The V-shaped gash they cut through the mountain is a proof of their industry, even if it failed of its full purpose. But it did lower the level of the lake--although this result was followed by an unforeseen catastrophe. The sudden release of the water through the channel opened for it left the precipitous shores of the lake unsupported. These shores then caved in, covering whatever treasure there might be in the center of the basin with masses of rock and earth, and thus placing a new obstacle in the way of the future miner. David and Raoul took the problem from a different angle. They abandoned the old cuttings of the Spaniards and planned a tunnel through the thinnest part of the mountain to the bottom of the lake. In this way they hoped to control the outflow of water, after which, they calculated, the recovery of the treasure would be a mere matter of placer mining. To do this they had boring machines and dynamite--modern giants, of whose existence the old Spaniards never dreamed.