James Small further advanced the design. Using mathematical methods, he eventually arrived at a shape cast from a single piece of iron, an improvement on the "Scots plough" of James Anderson of Hermiston. A single-piece cast-iron plough was also developed and patented by Charles Newbold in the United States. This was again improved on by Jethro Wood, a blacksmith of Scipio, New York, who made a three-part Scots plough that allowed a broken piece to be replaced. In 1837 John Deere introduced the first steel plough; it was so much stronger than iron designs that it could work soil in US areas previously thought unsuitable for farming.