 The natural gap in the North Downs north of Merstham is at an elevation of 120 metres (390 ft) above sea level.From this point run gently undulating slopes of significant chalk, sand, and some fuller's earth deposits, underlying regular (fertile) humus topsoil in the distance to Redhill's town centre (elevation around 75 metres or 250 feet).Similarly, Reigate High Street, further along the Holmesdale gap, is at an elevation of around 85 metres or 280 feet with a small hill immediately to the north where Reigate Castle is sited.