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The Bluff River Gorge is situated about an hour northeast of Hobart in the Swansea State Forest. This is a short scenic walk along one side of the gorge. Although the track is a little overgrown in some places, it is relatively easy to follow for those with some bushwalking experience. There are a couple of steep sections. This is one of a series of 3 caches placed to highlight different features of the gorge.
To get to the start of the walk you must first travel to Buckland, then turn off to the north onto the Buckland Road and travel for approximately 11km. There is a clear boundary between private property (open paddocks) and the state forest, which crosses the road in an obvious straight line, where the parking coordinates are located.
The track starts parallel with the fence line, and after a short distance you reach a small clearing where there is a fork in the track and a big tree with an arrow on it. The easier but slightly longer route is to take the right fork (in the direction of the arrow). This eventually leads to another small clearing where the gorge walk proper starts (see photo). You will need to leave the fire trail at this point and the trail to the gorge is narrow but defined. Head downhill to another not so obvious fork where the track branches off either around a tree (to GC2ZFA) or downhill, which is the way you need to go. Watch out for stinging nettles at this spot. After approximately 30 m there is another fork; you need to go straight ahead and make your way across the little creek, following the tape along the trail. The track ascends on the other side a short distance to GZ.
The sandstones of central and eastern Tasmania were formed in Permian and Triassic times (approximately 200-300 million years ago). The clean quartz sandstones are typical of the early Triassic; quartz is the dominant material, arising from the destruction and winnowing of older rock. The sandstone created in this period was not marine in nature, rather, the sedimentation occurred on windswept plains during periods of local flooding. Angular shaped grains of sand occur when there is minimal transport and tumbling of sand, whereas rounded grains suggest a long period of transport, tumbling and wearing of the individual grains. Deposition of sand also happened in dunes, billabongs and rivers. This created irregular consolidation and compaction of the sand, producing sandstones of varying quality. The colonial stonemasons were skilled at selecting the harder sandstone suitable for building.
In the latter Triassic period the sandstones were gradually overlaid by mudstone. There are a number of environmental forces which have shaped this sandstone to what it is today. The course of the Bluff River, over time, has carved into the softer areas and inconsistencies of the sandstone that was laid down. Although the gorge is deep, there are side cuttings in the gorge creating a fern leaf pattern of drainage. The tougher sandstone has survived in the form of ridges and cliffs. The remaining sandstone has been openly exposed to wind and rain, which has scalloped caves out of the softer sections of rock. There are also subtleties within the caves - fissures have been grooved deep into some of the softer lines of stone vertically, and even horizontally in some sections you can see the clear delineation between harder and softer layers of sandstone. There are visible round pebbles of harder volcanic rock in some sections. This often occurred during the later Triassic period. The colour of sandstone in this area ranges from white to tan and yellow, indicating varying quantities of the clear quartz with the amber coloured feldspar of the sand. There is also some iron oxide in this rock that adds an obvious reddish tint to the layers.
Claiming the EarthCache This is very straightforward once you have arrived at the listed coordinates. Observe carefully and answer the following questions and be sure to take a photo of you (or your team) at the site.
Approximately how big (in diameter) are the grains of sand at the bottom of the cave?
What is the approximate thickness of the sandstone shelves (where softer layers have been eroded) on the right side of the cave?
What colour are volcanic pebbles?
Send the answers, with a clear identification of the EarthCache, via the GC profile above and log your found. Logs without the corresponding correct answers and uploaded photo will be deleted.
Enjoy the EarthCache!
(No hints available.)
- S1 Fork 1Go right here
- S2 Track to GorgeFollow the tape
- S3 Fork 2When you reach this spot, go to the right downhill.....
- S4 Fork 3When you find the clearing with all the tape, veer to the right
- S4 TrackFollow the tape through here (you can see 2 in the picture)
- Sandstone Cave
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Coordinates are in the WGS84 datum