In the late 19th century Americans led the way in two architectural
forms: the country house and the skyscraper. The American shingle style
was developed out of the Queen Anne revivals of the English architects
Norman Shaw and William Burges. Organized in an informal, rambling fashion
around a large living hall, these houses show the development of the open
plan and easy transitions between indoors and outdoors that were to become
hallmarks of the best modern architecture of the early 20th century. The
vertical development of office buildings was made possible by the introduction
of the elevator, which was put into operation in New York City office buildings
in the 1850s. With the introduction of internal metal-frame construction
in William Le Baron Jenney's Home Insurance Company Building (1885, demolished
1931) in Chicago, the stage was set for the innovations of the Chicago
school of skyscraper design, headed by Louis Sullivan. Sullivan's Guaranty
Building (1894-95, Buffalo, New York) expresses in its cladding (sheathing)
the internal structure, achieving lightness with its emphatic verticality
and unity with its bold cornice.