At (53.4629, -2.4316), Chat Moss lies at the southern edge of the Lancashire Plain, an area of Bunter sandstones overlaid with marls laid down during the Late Triassic period. Those rocks are themselves overlaid by a layer of boulder clay deposited during the last ice age, about 10,000 years ago. The combination of the flat topography and the underlying clay resulted in extensive peat bogs developing along the Mersey Valley, and overflowing beyond the valley. The bogs in the area between the River Glaze in the west, and Worsley and Eccles in the east, to the north of what was the River Irwell – now the Manchester Ship Canal – are known collectively as Chat Moss.