River Mole in 1613. In John Speed's 1611 map of Surrey this stretch of the river is denoted by a series of hills accompanied by the legend "The river runneth under". However the river's name is unlikely to have derived from this behaviour: The "Oxford Dictionary of English Place Names" suggests that "Mole" either comes from the Latin "mola" (a mill) or is a back-formation from "Molesey" (Mul's island). In John Rocque's 1768 map of Surrey, the name "Moulsey River" is used. In common with much of the rest of the Weald, the earliest evidence of human settlement along the Upper Mole
River Mole Dorking drains an area of , of which approximately 60% is on Wealden Clay or Atherfield Clay, 20% is on Tunbridge Wells Sand and 20% is on greensand. Brickearth deposits are common in the valley around Betchworth and east of Dorking. The upper Mole catchment is dominated by a single broad terrace, which runs continuously from the entry to the Mole Gap as far south as Tilgate Forest. Above Meath Green (near Horley), the terrace corresponds to the flood plain of the river, however from this point downstream to Brockham, the river cuts a narrow trench no more than wide.