The springs emerge in boggy land at the base of the gravel banks, where deposits of blue boulder clay, known by the natives as "indiarubber clay", can also be found. Clay pits close to the farmhouses of Llangolman Farm (still visible) and Llyn are evidence that the clay was once extracted on a significant scale. The study by Jehu mentions that the clay pit at Llyn was down to a depth of 15 to 20 feet, and ladders were required to get in and out. His report goes on to state that the clay is bluish in color and very tough (hence the nickname indiarubber clay). The clay covers the valley bottom from Llyn to Llangolman Farm at a level of over 400 ft.