Lam Tsuen River is a good example
of a river eroding along line of weakness. Its main
stream follows the Lam Tsuen Fault, which runs northeast-southwest,
as many other major faults in Hong Kong.
Regarding bedrock: tuff is the dominant
rock in the north (Tai To Yan) and southwest (Ng Tung
Chai, Kadoorie Farm and Botanic Garden) of Lam Tsuen
River basin. Cuboidal blocks and toppled tors are
commonly found here.
To the east, the main rocks in the
southeast (She Shan and Lin Au) of Lam Tsuen River
are granodiorites, which typically weather easily,
resulting in a low terrain.