In contrast to Seidler's strongly European flavour of Modernism was the softer form practised by the so-called Sydney School of the 1950s and 1960s. This loose collection of architects, comprising, among others, Bill Lucas, Bruce Rickard, Neville Gruzman and Ken Woolley, favoured organic and natural houses, often built on steep slopes and hidden from view in natural bushland. These projects were largely on the city's North Shore, and to a lesser extent in the Eastern Suburbs. Following on from Walter Burley Griffin's work in the Sydney suburb of Castlecrag, this style of Australian architecture was visually sensitive to the environment and, like Griffin, often utilised natural local materials as structural elements.