The oil field had been extended from the valley of Oil Creek and its tributaries down the Allegheny River for fifty miles and probably covered 2,000 square miles. The early theory that oil followed the streams had been exploded, and wells were now drilled on the hills. It was known, too, that if oil was found in the first sand struck in the drilling, it might be found still lower in a second or third sand. The Drake well had struck oil at 69½ feet, but wells were now drilled as deep as 1,600 feet. The extension of the field, the discovery that oil was under the hills as well as under streams, and to be found in various sands, had cost enormously. It had been done by “wild-catting,” as putting down experimental wells was called, by following superstitions in locating wells, such as the witch-hazel stick, or the spiritualistic medium, quite as much as by studying the position of wells in existence and calculating how oil belts probably ran. As the cost of a well was from $3,000 to $8,000,[4] according to its location, and as 4,374 of the 5,560 wells drilled in the first ten years of the business (1859 to 1869) were “dry-holes,” or were abandoned as unprofitable, something of the daring it took to operate on small means, as most producers did in the beginning, is evident. But they loved the game, and every man of them would stake his last dollar on the chance of striking oil. With the extension of the field rapid strides had been made in tools, in rigs, in all of the various essentials of drilling a well. They had learned to use torpedoes to open up hard rocks, naphtha to cut the paraffine which coated the sand and stopped the flow of oil, seed bags to stop the inrush of a stream of water. They lost their tools less often, and knew better how to fish for them when they did. In short, they had learned how to put down and care for oil wells. Equal advances had been made in other departments, fewer cars were loaded with barrels, tank cars for carrying in bulk had been invented. The wooden tank holding 200 to 1,200 barrels had been rapidly replaced by the great iron tank holding 20,000 or 30,000 barrels. The pipe-lines had begun to go directly to the wells instead of pumping from a general receiving station, or “dump,” as it was called, thus saving the tedious and expensive operation of hauling. From beginning to end the business had been developed, systematised, simplified.