 The extensions from Rickmansworth to Aylesbury and Chesham were designed by Charles Liddell and built by contractor James Firbank . Rather than follow the valley of the River Chess , which would have been the most convenient route to Chesham , the route out of Rickmansworth was intentionally built on higher ground to reduce the steep climb over the Chilterns towards Aylesbury , and thus rose steadily from Rickmansworth to a hilltop station at Amersham . At Chalfont Road station ( renamed Chalfont & Latimer in 1915 ) , near Chalfont St Giles , the line to Chesham split from the line to Aylesbury . With a total length of 3 miles 56 chains ( 3 mi 1 @,@ 232 yd ; 5 @,@ 955 m ) , the single @-@ track Chesham branch ran alongside the Aylesbury line for a short distance , before curving down the slope of the Chess Valley at a gradient of around 1 in 66 . Chalk from the railway 's cutting along the Chess Valley was used to build an embankment to bring the railway into the town centre . Bridging the watercress beds of the Chess Valley proved problematic , and the cost of the line exceeded its estimate . Additional costs were incurred by the laying of temporary track in early 1889 to allow the directors of the MR a trial trip along the route . 
