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Viewing swaag.org website implies consent to set cookies on your computer. Full details Swaledale and Arkengarthdale Archaeology Group
Registered Charitable Incorporated Organisation Number 1155775
SWAAG Honorary President:
Tim Laurie FSA

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 *****SWAAG_ID***** 898
 Date Entered 09/10/2015
 Updated on 09/10/2015
 Recorded by Tim Laurie
 Category Geological Record
 Record Type Geological HER
 Site Access Public Access Land
 Record Date 08/10/2015
 Location Birkdale Tarn
 Civil Parish Muker
 Brit. National Grid NY 852 018
 Altitude 488m
 Geology Namurian sandstone bedrock with glacial striae and massed tube fossil fragments exposed at low water on the southern side of the 'Tarn'.
 Record Name A perambulation of Birkdale Tarn at low water, a mining reservoir with landscape interest.
 Record Description Birkdale 'Tarn' is in fact a small reservoir originally dammed to provide water and probably also to provide hydraulic power to the pumps at the deep mines at the lower end of Great Sleddale above Stone Houses. At low water, the surface of the glacially smoothed and striated bedrock is exposed on the eastern shore of the Tarn. Of some further palaeontological interest are the massed fossil tube fragments which cover a short length of the beach of the Tarn. Since these loose tube fragments are only concentrated on the shore within a length of 25m, the strata from which they originate must have a limited exposure. These solid tubular fragments, which are smooth surfaced and average 15mm diameter, approximately, and not more than 75mm in length, are of silica and clearly harder than the shale or sandstone within which they were deposited. The strata from which they had eroded must now exist below water level, as the rock with these tubes in situ is nowhere visible. The shrunken waters of the Tarn are retained by a very substantial dam , see photographs. When in use the waters could have been considerably deeper, as the present level of the Water is well below the level of the base of the Tarn.
 Dimensions See photographs
 Additional Notes The waters of the Tarn are, today, shallow, windswept and very acid, without any sign of aquatic plants or of the gulls which once nested here. The only birds visible on our visit were a pair of Goosanders.
 Image 1 ID 6486         Click image to enlarge
 Image 1 Description Birkdale tarn at low water
 Image 2 ID 6487         Click image to enlarge
 Image 2 Description Birkdale tarn, first sight from the east
 Image 3 ID 6488         Click image to enlarge
 Image 3 Description Birkdale tarn, the eastern shore. Mallerstang Edge with High Seat in distance.
 Image 4 ID 6489         Click image to enlarge
 Image 4 Description Glacial striae on exposed bedrock previously under peat, East Shore
 Image 5 ID 6490         Click image to enlarge
 Image 5 Description Glacial striae
 Image 6 ID 6491         Click image to enlarge
 Image 6 Description 
 Image 7 ID 6492         Click image to enlarge
 Image 7 Description Fossil tube fragments like these cover a short 25m length of the eastern shore
 Image 8 ID 6493         Click image to enlarge
 Image 8 Description Detail of the fragments
 Image 9 ID 6494         Click image to enlarge
 Image 9 Description Eileen at the eastern Shore. Fossil fragments cover the darker areas of the beach.
 Image 10 ID 6495         Click image to enlarge
 Image 10 Description Two very small streams feed into the northern end of the Tarn. The silver sand was previously used to sharpen scythes.
 Image 11 ID 6496
 Image 11 Description Birkdale tarn, the peat embanked western shore.
 Image 12 ID 6497
 Image 12 Description Birkdale tarn. The substantial and stone slab surfaced dam.
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