Within the context of Cenozoic climatic and glacial history, grain size, mineralogy and sand grain surface textures have been used to investigate sources of glacial drift. Components of Precambrian crystalline bedrock, friable, Hadrynian or younger Double Mer sedimentary rocks, offshore Paleozoic sediments and Tertiary-Quaternary mudstones and sands have been identified in the drift. The sand fraction appears to have evolved through a complex history of several sedimentary cycles beginning with chemical, fluvial and glacial erosion of grains from the Double Mer Formation. There then followed, proglacial silica precipitation on grain surfaces, reworking and Pliocene to Pleistocene deposition in a shallow marine delta. In the late Pleistocene the delta was exumed allowing subaereal weathering, shallow marine-aeolian reworking, glacial modification and quartz crystal overgrowths to further modify the grains.