Dumble's Wooded Ravine EarthCache
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The name Jumbles appears during the 19th century, it is a variation
of 'dumbles' which is a northern term for a ravine like valley with
wooded sides down which tumbles a fast flowing stream.
This valley is formed by a line of three reservoirs to the north of Bolton, two of which (Entwistle and Wayoh) supply Bolton with the majority of its drinking water. Each is surrounded by extensive woodland, much of which is in the form of conifer plantations. Originally the valleys in which these reservoirs are sited fed the Bradshaw Brook, which became a local focus of industrial activity. The success of textiles and bleaching provided the stimulus for reservoir construction in the area. Entwistle was the first in the 1830s and indeed one of the first in the country at such a scale, followed by Wayoh thirty years later, and more recently by Jumbles in 1971 to provide compensation water to Bradshaw Brook. The reservoirs are now a focus for recreation and nature conservation, with walking, fishing and informal pursuits located at Entwistle and Wayoh, and the County Park centred around Jumbles Reservoir offering more formal recreation. A feature of particular note is the Armsgrove Viaduct which carries the Bolton to Blackburn railway over the Wayoh Reservoir. The valley includes the attractive settlements of Chapel Town and Turton.
The Reservoir Valleys follow faults in the bedrock along a roughly south-east to north-west axis. The whole area was heavily glaciated during the Pleistocene and the retreat of the glaciers formed a deep overflow channel from Brinscall to Horwich. This over deepened valley is now occupied by the Anglezarke and Rivington reservoirs.
The valleys contain much evidence of past mining and quarrying, especially for sandstone.
The Leicester Mills sandstone quarry at Rivington with its high
sandstone edge is now an important landscape feature and
recreational resource. Important semi-natural woodlands survive,
particularly in the Rivington and Belmont valleys. Farmland and
embankments adjacent to the reservoirs are often ecologically
important; species-rich hay meadows and pastures and grasslands
contain nationally rare plants.
Faults are discontinuities in the bedrock that arise from tectonic forces causing the rocks in the earth's crust to shear and move displacing one side of the fault relative to the other. Once the rocks have been broken, the fault plane becomes a permanent zone of weakness that often enhances the permeability of the surrounding host rock by providing fractures through which water can move. Depending on the type of rock involved and the nature of the fluids moving along the fault plane, some faults can become mineralized and act as a barrier to flow forcing groundwater to seep out at the ground surface whereas other faults remain open allowing water to flow freely along the fault plane. Faults can be a few millimeters to several kilometers in width and range from a single fault plane to a wide zone of highly fractured rock that contains an anastomosing, interwoven network of permeable, interconnected fractures. There are several clues that provide evidence for faulting in the field. These include offset between rock types on opposite sides of the fault plane, folding of the host rock due to drag along the fault, brecciated rock within the fault zone and striated fault plane surfaces, highly fractured rock adjacent to the fault, and extensive mineralization suggesting past or recent fluid movement. Most of the quarry face at the northern end of the reservoir is composed of water-borne mud and sand grains compressed by their own weight over millions of years, to form sedimentary rocks. They are separated in places by seams of
poor grade coal resulting from environmental changes. The rocks are only a tiny exposure of a deposit of similar sediments laid down
the mouth of a huge river some 300 million years ago. The lowest
layer of course-grained sandstone was deposited from fast-moving
water. When the channel changed position fine-grained mud settled
out of the slow-moving water. Repetition of such events produced
the different-textured layers visible today.
To log this earthcache upload a photo of you or your GPSr with the rock face in the background and E-mail me the answer to the following questions
1) Estimate the height of the jointed sandstone layer
2) Give me the name of the prominent layer above the jointed sandstone
3) What colour is the top layer of the cliff
Any logs with no photograph will be deleted please do not include your answers in your log.
All of the reservoirs, and particularly Jumbles, Wayoh, Delph and Belmont and Rivington are important to wintering wildfowl. Belmont is also significant for the breeding wader assemblage associated with adjacent in-bye pastures. The woodlands and plantations are also valuable for breeding birds including woodcock, redstart and pied flycatcher.
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