The given coordinates will take you to the stunning Black Rock Waterfall on Dartmoor's River Lyd.
For this Earthcache we will investigate the name of this Waterfall which is also linked to the nearby Black Rock.
As you will have already seen Dartmoor is formed from Granite both above and below the surface of the ground.
The Granite you see around you was formed about 280 million years ago from molten rock at a temperature of 900-1000° C.
The minerals which make up granite crystallised as closely interlocking grains as they cooled forming the hard rock.
Granite is formed by 3 main minerals:
- QUARTZ Translucent slightly greyish looking grains
- FELDSPAR Large White crystals
- BIOTITE Dark Brown glistening flakes
As the still hot but solid Granite continued cooling cracks and fractures known as joints appeared in the rock. Hot water moving through the cooling joints led to deposits of Quartz and a black mineral called TOURMALINE forming within the granite. TOURMALINE mostly appear as black veins in the granite.
Kaolinisation has taken place in parts of the moor. This is where the circulation of hot water within the granite has caused Kaolin ( China Clay ) found in the Feldspar to erode away.
The rocks and boulders around the moor were mainly created during the ice age between 2 million and 10,000 years ago. The extreme cold temperatures broke the granite up.
TO LOG THIS EARTHCACHE PLEASE LOOK AT THE GRANITE IN THE ATTACHED PHOTO AND THE GRANITE ROCKS THAT MAKE UP THE WATERFALL. THE PHOTO ATTACHED TO THIS LISTING IS TO ASSIST YOU.
YOU WILL NOTICE THAT THE GRANITE IN THE RIVER LOOKS DARKER IN COLOUR.
1. LOOK CAREFULLY AT THE GRANITE IN THE WATER. DOES IT LOOK DARK? IF SO WHY?
a) THE ROCK IS WET AND THEREFORE DARKER
b) THERE IS BLACK ALGAE GROWING ON THE ROCK
c) MUCH OF THE WHITE KAOLIN WITHIN THE FELDSPAR HAS BEEN ERODED AWAY AND THEREFORE GIVES THE ROCK A DARKER APPERANCE.
d) THERE IS INCREASED DEPOSIT OF TOURMALINE IN THE ROCK
e) THERE IS INCREASED BIOTITE IN THE GRANITE.
2. DESCRIBE THE OVERAL SHAPE AND TEXTURE OF THE GRANITE IN THE WATER AND THE GRANITE ON THE RIVER BANK. TRY TO EXPLAIN THE DIFFERENCES YOU CAN SEE. IF YOU WISH PLEASE TAKE A PHOTO OF YOURSELF, GPS OR GEOHOUND AT THE FALLS AND UPLOAD IT WITH YOUR LOG.
PLEASE DO NOT POST ANSWERS WITHIN YOUR LOG
PLEASE MAIL OR MESSAGE ME YOUR ANSWERS. THEN LOG AS FOUND. I WILL REPLY AS SWIFTLY AS I CAN. Please note for question 1 any combination of the given answers may be given .
