The skew means about 40 % more stone was used. Usually skewing is achieved by placing of the piers but here they are parallel to the river's flow and each span is skewed, being built up of four separate arch rings, each placed a little ahead of its neighbour and each at right angles to the pier. The distribution of forces in a skew arch are more complicated than in a square one and this method of Mitchell's was possibly a way of breaking it down into simpler square arches. [1]