`Ornamentation,' says Ruskin, `is the principal part of architecture.' It is that part, he says in another place, which impresses on a building `certain characters venerable or beautiful, but otherwise unnecessary." Sir George Gilbert Scott amplified this surprising statement when he recommended to architects the use of the Gothic style, because its `great principle is to decorate construction.'

Modern movement has not grown from one root. One of its essential sources, it has been shown, is William Morris and the Arts and Crafts; another was Art Nouveau. The works of the nineteenth-century engineers are the third source of our present style, a source as potent as the other two.

Engineering architecture in the nineteenth century was largely based on the development of iron, first as cast iron, then as wrought iron, later as steel. Towards the end of the century, reinforced concrete appears as an...