Editing River Mole (section)

===Upper Mole <span style="display:none">(geology)</span>===

The Mole rises south of Rusper in West Sussex, where an outcrop of the [[Wealden Group|Hastings Beds sandstone]] dips below the impermeable [[Weald Clay]].<ref name=MAls_2013/> From the source to [[Dorking]], the river drains an area of {{convert|340|km2|sqmi|abbr=on}}, of which approximately 60% is on Wealden or Atherfield Clay, 20% is on Tunbridge Wells Sand and 20% is on [[greensand]].<ref name=physiography/> [[Brickearth]] deposits are common in the valley around Betchworth and east of Dorking.<ref>{{cite web |url= http://www.surreymuseums.org.uk/collections/geology/geosur.html |title= The geology of the county of Surrey |date= November 2006 |work= Geological Collections in Surrey Museums |publisher= Surrey Museums Consultative Committee |access-date= 6 February 2012 |url-status= dead |archive-url= https://web.archive.org/web/20120229212044/http://www.surreymuseums.org.uk/collections/geology/geosur.html |archive-date= 29 February 2012 |df= dmy-all }}</ref>

The upper Mole catchment is dominated by a single broad terrace, which runs continuously from [[Tilgate|Tilgate Forest]] to the entry to the Mole Gap. 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 {{cvt|150|m|yd}} wide. A similar trench is runs up several of the Mole's tributaries, notably along Deanoak Brook which follows a local [[strike and dip|strike]]. The presence of the trench protects the land from flooding, rendering it suitable for [[agriculture]].<ref name=physiography/>