Ma Shi Chau Special Area covers 61 hectares of land. It consists
of 4 islands in the Tolo Harbour, namely, Ma Shui Chau, Centre
Island (also known as A Chau), Yeung Chau and the unnamed island at
about 100 metres off the northeast shore of Yim Tin Tsai peninsula
near Sam Mun Tsai New Village.
This Special Area consists of some oldest rocks in Hong Kong and is
rich in geological and geomorphological features such as folding,
faults, unconformities and wave-cut platforms. It also is a place
of special interest and importance by reason of their flora, fauna,
geological, cultural or archeological features. Fossils of corals,
shells and plants are found in Central Island and Ma Shi Chau.
Yueng Chau is an island of igneous rock made up of granodiorite and
is totally unspoiled. The unnamed island is a nesting sit for
egrets and has mature woodlands.
These four islands have not been disturbed by any development.
Since 1999, the Special Area is managed by the Country and Marine
Parks Authority for nature conservation, in particular conserving
the valuable geological features, and outdoor education purposes.
Without permission of the Country and Marine Parks Authority, no
person shall excavate any rocks, fossils or collect any specimens
in Special Area.
CARRIES ON THE OBSERVATION IN MA SHI CHAU, MAY WALK ALONG THE
ISLAND EDGE, appreciates to relieves the tuff and the
conglomerate the unconformity, the nature cold thermal cycle, the
fault break and shifting, the maritime vegetation, the difference
corrodes, the dike and the quartz-porphyry, the rock does not crimp
and so on many kinds of phenomena, is a research stratum, the
deposition characteristic and each kind of geologic structure
extremely good place.
- A tale of two rocks - the unconformity of tuff and
conglomerate
Igneous rock is formed from solidified magma. Tuff is formed
from volcanic ash ejected into the atmosphere but which eventually
settled into the ground surface. Sedimentary rock is formed by the
accumulation and consolidation of sediments. Conglomerate is a kind
of sedimentary rock characteristically composed of rounded pebbles
cemented by sand and mud.
- Nature's coloring
Underground water carrying insoluble iron oxide seeped through
fractures called joints leaving ion oxide to settle. The passage of
underground water also rounded the corners and edges of the joints.
Subsequently the weathering and erosion processes exposed this once
buried geological feature. Consistent exposure to the sun created a
rusty appearance in the rocks.
- Faults, the fractured and displaced rocks
The result of tensional or compressional forces originating from
tectonic movement creates a fault line with rock fractured and
displaced. Faults affected the stability of large-scale
construction. The effect of earthquake on an area with faults would
be disastrous.
- The secret of age - the oldest rock in Ma Shi Chau
The oldest rock in Ma Shi Chau is located on its southeastern
coast. It was formed during the Permian period (about 280 to 225
million years ago). The fossils they contain primarily determine
their ages. Some organisms are known to have existed within a
specific period and had a broad geographical distribution. The key
index fossils found here are ammonites, bivalves, brachiopods, and
lamellibranches, which only survived up to the Permian era, one of
the earliest geological age for sedimentary rocks formed in Hong
Kong.
- Cheese on pizza - quartz veins
There are some thin white masses and stripes in the rocks, some
just look like the cheese layer on top of pizza! They are made up
from mineral called quartz. The rocks themselves are fractured
quartz porphyry. In the past, a hot solution migrating along the
fractures and silicon dioxide precipitated out of the solution
along the walls.
- Beach and rubbish
A beach is a feature built up from unconsolidated sediments,
which are brought ashore by wave action and settle along the
shoreline. Apart from sand, gravel and pebble, it can also find
seashells and rubbish along the beach.
- A struggle between lives and the environment - seashore
vegetation and beach
In order to stop the beach deposits carried further inshore, the
coastal vegetation developed prop roots which broaden the base and
provide stability. Plants commonly found along the shoreline of Ma
Shi Chau are Cuban Bast (Hibiscus tiliaceus), screw place (pandanus
sp.), Cerbera (Cerbera manghas). Some mangroves such as Kandelia
candel, Aegiceras corniculatum can be found. Coastal plants must be
specially adapted to survive in this harsh environment with salty
water, wave erosion, and poor support from loose substrate. Salt
glands are present in leaves of Aegiceras corniculatum to secrete
the absorbed salts.
- Dragon diving into the sea - differential erosion on
shale
It is the result of differential erosion on a kind of
sedimentary rock called shale, which is a sedimentary rock composed
of clay particles. During sedimentation, the clay particles settle
intermittently. Every time a new flood of clay settles, apparent
sedimentary boundaries are formed. Eventually, a fine textured
sedimentary rock is formed with well-stratifies layers. Later,
earth movement tilted and exposed the shales which are composed of
alternating resistant and nonresistant layers at which the
nonresistant units were eroded while the resistant layers were left
standing as long asymmetric ridges.
- Dyke and quartz porphyry
A dyke is a vertical intrusion of once molten material into a
fracture, but the dimensions of dykes are much more extensive than
veins. The intrusive material in this dyke is quartz porphyry.
Since weathering has been very intense in this area, its color has
become darkened.
- Like a rolling stone - shale boulders
These rocks are black and rusty in color. When the underground
water seeps through the fractures, the insoluble iron oxide and
manganese oxide are precipitated along the inner wall surface. Iron
oxide and manganese oxide change the rocks to a rusty and black
appearance respectively.
- Fool's gold in concretion
Microorganisms consumed most oxygen in the sludge to degrade the
organic materials while the weak water current could not replenish
the oxygen in the water. This encouraged sulphur and iron
containing compounds to react and produce pyrite, an iron sulphide
crystal which is gold in color. The pyrite accumulated around a
foreign solid object and eventually a rounded and symmetrical
concretion was formed.
- The formation of wave-cut platform
Ma Shi Chau is frequently subjected to wave erosion. Waves act
like a horizontal saw cutting a notch into the bedrock at sea level
and eventually forming a wave-cut cliff. As erosion continues, the
cliff recedes and a terrace is formed which is called a wave-cut
platform.
- Mighty nature
Folds are warps in rock layers caused by compressional forces.
When pressure stronger than the limit the rock layers can withstand
is applied, rocks will be cracked and displaced.
How to get there?
- Take bus
#74K from Tai Po Market Railway Station Bus Terminus
- Take minibus #20K from Tai Po Market Railway Station MinisBus
Terminus
To log this cache, please send the answer of the following
questions to owner:
1. Who and when was inaugurated that Ma Shui Chau Special
Area?
2. In order to ensure safety during the field studies, please state
any two guidelines should be observed?
3. A sediment deposits geological feature is built up and join from
Yim Tin Tsai to Ma Shi Chau. What is that geological feature
called?
4. Please state the reason for so much rubbish deposited on Ma Shi
Chau. (Standard answer could be found inside the Park.)
5. (Optional) Post any 2 photos of your GPSr with Ma Shi Chau
Special Area scenery in the background.
Please don't post the answer into the log.
(P.S. An EarthCache site is a special place that people can
visit to learn about a unique geoscience feature or aspect of our
Earth. The treasure is the lessons people learn about our plant
when they visit the site. Any irrelevant misleading information
will be deleted.)