ABSTRACT
This Chapter discusses lists of all of the dykes and diatremes reported to exist in the Greater Sydney Region. Geophysical methods may, in certain areas, be successfully applied to detect dykes. Pittman published a geological map of an area little larger than the Greater Sydney Region and on it he plotted all of the then known igneous intrusions. Weathering by atmosphere, rain, groundwater, sea water etc. tends, near Sydney, to cause many dykes to become almost completely converted to clay and oxide minerals. In a few places the dykes are less weathered than the country rock and so form positive features an inland example occurs at Luddenham, one on an intertidal rock platform occurs at Long Reef Point. Sills, laccoliths and lopoliths must all be fed by one or more feeder channels which are seldom seen and at depth are probably dykes, lava flows may be associated with plugs or dykes.
