https://www.geographysouthwest.co.uk/wp-content/uploads/2021/10/PTV-Baggy-Point-Erratic.pdf
The Baggy Point erratic is a large granulite gneiss boulder that has been carried by ice from Western Scotland. It weighs some 50 tons, but sea erosion and encrusted lichens make it a little tricky to spot.
The Baggy boulder is one of a suite of over twenty glacial erratics (according to Paul Madgett, there are 37 of them) that can be found along this stretch of north Devon coastline. Two of them are quite accessible (this one at Baggy Point, and another at Saunton are relatively easy to identify, but most of the others are much smaller and quite difficult to find.
As at Saunton, the Baggy erratic sits on a wave cut platform created from the local rocks. At this location, the foreshore consists of Baggy sandstones that overlie the Upcott slates that form Baggy Point itself. These sedimentary beds of mudstones, siltstones and sandstones were formed in the Devonian Period between 359 to 372 million years ago. They were deposited as horizontal layers on the sea bed, but have since been uplifted and contorted, and hardened into vertically aligned layers. The sea has since carved this rock into sharp ridges and ancient fault lines are marked by long, straight and deep gullies, created where less-resistant beds have been eroded at a faster rate.
Behind the erratic boulder is a clear exposure of an old cliff line formed from Pleistocene raised beach material, or sand rock, that was created in the Ipswichian interglacial. This provides clear evidence of how sea levels at this location have been at different heights in the past.
The Baggy boulder is one of a suite of over twenty glacial erratics (according to Paul Madgett, there are 37 of them) that can be found along this stretch of north Devon coastline. Two of them are quite accessible (this one at Baggy Point, and another at Saunton are relatively easy to identify, but most of the others are much smaller and quite difficult to find.
As at Saunton, the Baggy erratic sits on a wave cut platform created from the local rocks. At this location, the foreshore consists of Baggy sandstones that overlie the Upcott slates that form Baggy Point itself. These sedimentary beds of mudstones, siltstones and sandstones were formed in the Devonian Period between 359 to 372 million years ago. They were deposited as horizontal layers on the sea bed, but have since been uplifted and contorted, and hardened into vertically aligned layers. The sea has since carved this rock into sharp ridges and ancient fault lines are marked by long, straight and deep gullies, created where less-resistant beds have been eroded at a faster rate.
Behind the erratic boulder is a clear exposure of an old cliff line formed from Pleistocene raised beach material, or sand rock, that was created in the Ipswichian interglacial. This provides clear evidence of how sea levels at this location have been at different heights in the past.
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This massive erratic must indeed have been emplaced by ice, but I disagree with Paul on a couple of points. First, the shore platform on which the erratic rests has to be older than Ipswichian -- and indeed, evidence from all around the Bristol Channel suggests that although the raised beach deposits may well be of Ipswichian age, the rock platform is certainly older -- and indeed may be a composite feature, cut and refreshed during a number of older interglacial episodes.
Secondly, the idea of emplacement by floating ice is no longer tenable. An erratic of this size cannot have been transported on slabs of floating sea ice. It must have been carried either in an iceberg or in a large and deep chunk of brash ice -- and that means deep water. Deep water cannot have existed here at a time of iceberg transport, because when the Celtic Sea was awash with the debris of glacier disintegration, the sea was not here at all -- it was probably at least 100m lower down, and most of the Bristol Channel was dry land.
So the erratic must have been dumped from a melting glacier -- but which glacial episode are we talking about? Anglian? Wolstonian? Happisburgh? The jury is still out.
See also:
1 comment:
Fascinating stuff this..... in not just this Post but also in the other two you posted at the same time on erratics, including the newly- discovered Gower coast one which is being analysed. Have a read of the WHOLE lyrics, and ALL verses, of Bob Dylan's "The Times They Are a Changin'" Best to substitute, of course, "Stonehenge experts and geologists" for " Senators and Congressmen", etc!
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