Permian rocks outcrop only in the Bacchus Marsh area, within the Melbourne Region and are exclusively of sedimentary origin. Outcrops of the Permian sediments are restricted to road cuttings, stream channels and areas of major soil erosion. Most outcrops of the Bacchus Marsh Formation, within the Bacchus Marsh area, are confined to the east-west trending Ballan Graben which is bounded on the northern side by the Greendale, Coimadai and Gisborne Faults and on the southern side by the Spring Creek Fault. The complexity of lithologies and weathering patterns with the Permian sequences and the occurrence of basal unconformity surfaces emphasise the need for individual site analysis prior to engineering decisions affecting areas of Permian outcrop. Published details of outcrop sections are few and demonstrate the complexity of lithologies and their facies interpretations. Siliceous weathering crusts occur on some outcrops such as the cliffs in Werribee Gorge developed in dominantly sandy lithologies.