The ‘Beccari Discovery Trail’ at Kampung Matang winds around the foothills of Matang Range for a distance of about 3.2 km up the hillside following the story of Italian botanist Odoardo Beccari who made a scientific discovery on plants and insects during the Rajah Charles Brooke’s reign. The mostly tar-sealed route starts from the old cart track at Kampung Matang to a fork about 2.8 km away where the Sree Jadamuniwaran Temple is located. The left fork is a continuation of the tar-sealed road right up to the Sri Maha Mariammam Hindu Temple while the right fork is a jungle trail leading to the site of Beccari’s field house Vallombrosa.
The road is cut into the hillside following the contour at a gentle gradient. The cuttings reveals the geology of the Matang Range which is mainly sendimentory rock that had been uplifted. At GZ, take a closer look at the cutting to look for the object of interest today.
What are we looking for?
Within the matrix (surround rock that all looks the same) of the crumbly sedimentary rock – you will observe some darker, rounder shaped rocks within the shale matrix. These are the subject of this Earthcache.
As you look around this old road cutting, you should be able to see a good few of these roundish rocks within a 25 to 50 centimetre radius. Now here is the object of the Earthcache. What are they and how were they likely form?
In geological speak, these roundish things are known as either CONCRETIONS or NODULES. But what is the difference between the two?
Concretion :
Concretions are aggregates that occur within sedimentary rocks (like shales and sandstones) and are composed of inorganic material (i.e. they are also “rocks” or minerals). They are often spheroidal or discoidal (disc like) in shape. Generally they are composed of a single mineral and so are often uniform in structure and colour (except for exposed and weathered pieces). Impurities can make colour differences but these are often seen in a layer or band within the concretion.
Concretions are usually formed after sediment is buried but before it undergoes a physical change and becomes rock, which is a process called diagenesis. Concretions form when minerals precipitate and cement sediment around a nucleus, which is usually organic. Sometimes concretions will form around a foreign object in the original sediments. So it is not uncommon to “break open” a concretion and find a fossil inside. They are not fossils themselves, but may contain fossils and are often used as indicators for fossil hunters in areas that are rich in fossils. So concretion mostly form around an object (it may be a pebble, a leaf or a bone).
Nodules:
Nodules appear very similar to concretions, and the terms are often used interchangeably. They differ in that they are not formed around something but are a “replacement” of a mineral within the rock matrix. So what one sees is a very different mineral from the surrounding rock (e.g. a manganese or pyrite nodule within a siltstone or coal). Nodules are also often associated with metamorphosed rocks too.
Your tasks to claim this Earthcache !
In order to substantiate your visit and be able to claim this Earthcache, a number of questions need to be answered and submitted to the cache owner.
a) Look around the site and find a few of these geological “oddities” so that you can analyse them. Look at the shape, colour and the way that they have weathered. Describe them.
b) Based on your answers in “a” above, do you think these are CONCRETIONS or NODULES? Why do you say this?
c) How many balls do you see at the site? How many balls are intact?
d) Describe any other interesting things you saw or experiences you had on site (you can add these to your log too for others to enjoy too). Photos are always welcomed in the logs.
NOTE: You may log your visit prior to approval, but e-mail submissions that do not meet the above criteria will be deleted.