 The ice sheet, which stopped around present-day Finchley, deposited boulder clay to form Dollis Hill and Hanger Hill.Its torrent of meltwater gushed through the Finchley Gap and south towards the new course of the Thames, and proceeded to carve out the Brent Valley in the process.Upon the valley sides there can be seen other terraces of brickearth, laid over and sometimes interlayered with the clays.