HARLECH 5 - Geology and Gold
Harlech Castle itself sits on Rhinog Grits, essentially a coarse sandstone.
At the base of cliff, under the castle there are alternating layers of green slate and sandstone
Indeed all the rocks of the Harlech region consist of conglomerate, sandstone, and mudstone( now slate), which have been compressed into large folds, raising them into a huge dome.
Wonderfull examples of folds can be seen clearly on the approach road to the Briwet Bridge over the Afon Dwyryd
The softer mudstones and slate are subject to significant erosion from weathering leaving the harder sandstone as the rugged Rhinog mountains.
The rocks in this "Harlech Dome" are Cambrian, while the surrounding rocks of Snowdon and Cadair Idris (across the estuary in the picture above) are from the Ordovician age. Gold mining was conducted around the dome's south eastern edge near Dolgellau (at the head of the pictured estuary). Here the Clogau shale lies exposed with its occasional quartz vein and auric contents.
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The Tal y Llyn valley on the south side of Cader Idris is another local feature of great geological interest and significance.
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For more information about Harlech and the surrounding area - click on the picture or on
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