He appreciated the fact that it was a serious and gigantic problem, but was fully satisfied that he could solve it. He first planned a great magnetic survey of the East, with the object of locating large bodies of magnetic iron ore. This survey was the greatest and most comprehensive of the kind ever made. With a peculiarly sensitive magnetic needle to indicate the presence of magnetic ore in the earth, he sent out men who made a survey of twenty-five miles across country, all the way from lower Canada to North Carolina. Edison says: "The amount of ore disclosed by this survey was simply fabulous. How much so may be judged from the fact that in the three thousand acres immediately surrounding the mills that I afterward established at Edison, New Jersey, there were over two hundred million tons of low-grade ore. I also secured sixteen thousand acres in which the deposit was proportionately as large. These few acres alone contained sufficient ore to supply the whole United States iron trade, including exports, for seventy years." Given a mountain of rock containing only one-fifth to one-fourth magnetic iron, the broad problem confronting Edison resolved itself into three distinct parts--first, to tear down the mountain bodily and grind it to powder; second, to extract from this powder the particles of iron mingled in its mass; and third, to accomplish these results at a cost sufficiently low to give the product a commercial value. From the start Edison realized that in order to carry out this program there would have to be automatic and continuous treatment of the material, and that he would have to make the fullest possible use of natural forces, such as gravity and momentum. The carrying out of these principles and ideas gave rise to some of the most brilliant engineering work that has ever been done by Edison. During this period he also made many important inventions, of which several will now be mentioned. As he proposed to treat enormous masses of material, one of the chief things to be done was to provide for breaking the rock and crushing it to powder rapidly and cheaply. After some experimenting, he found there was no machinery to be bought that would do the work as it must be done. He was therefore compelled to invent a series of machines for the purpose. The first of these was an invention quite characteristic of Edison's daring and boldness. It embraced a gigantic piece of mechanism, called the "Giant Rolls," which was designed to break up pieces of rock that might be as large as an ordinary upright piano, and weighing as much as eight tons.