This memoir traces the geological history of the district from the muddy seas and volcanicity of the early Palaeozoic of 450 million years ago, via the deserts of the Trias and the shallow tropical and subtropical seas of the Jurassic and Cretaceous, to the last glaciation 18,000 years ago, when much of the district was covered by ice. Finally, it records the history of the period after the retreat of the ice when temperate climates returned and the broad hollow that was to become Fenland and the Wash became progressively filled with freshwater peats, estuarine muds and marine sands as sea level rose in response to the melting of the ice.