Lai Chi Chong
Giant’s Washboard (Half-day course)
On the southeastern shore of Tolo Channel in the Eastern New Territories, a set of Early
Cretaceous volcaniclastic sedimentary rock strata called Lai Chi Chong Formation are distributed
around rural Lai Chi Chong and nearby coastal areas. They are “younger” than the sedimentary
rock of Ma Shi Chau but “older” than that of Tung Ping Chau. Research has shown that this region
has rather complicated geological setting and rock types, with Mesozoic volcaniclastic
sedimentary rocks, tuff, rhyolite and Paleozoic sedimentary rocks occurring locally. The uneven
stratum on the foreshore near the Lai Chi Chong pier is volcanic ash sedimentary rock.
Displaying very distinctive foldings, faults and bedding structure, it is an ideal location for
geological study.
Major outcropped sections of Lai Chi Chong Formation can be found on the beach west of Lai Chi
Chong pier. Although less than 200m wide, these sections manifest extremely complicated rock
properties that include tuffite, tuffaceous sandstone, siltstone, coarse ash crystal tuff,
eutaxitic fine ash tuff and porphyritic rhyolite in current bedding. Bedding development is
excellent with a wealth of visible sedimentary structures, such as current bedding, graded
bedding, convolute bedding and subaquatic slump. Signs occurring from folding, fault and
discordance of strike directions are also clearly noticeable.
