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Friday, 16 January 2015

Baggy Point erratic at +80m altitude


 Bad quality photo, but this is the 50-tonne erratic at Freshwater Gut.  This one is on the shore platform close to sea level.

I came across this record of erratics in the Croyde Bay area.  It's interesting that a Scottish origin is assumed for at least two of these well-known erratics.

"High on the crest of these same cliffs (+80m OD) sits a large isolated 500kg block of epidiorite (SS 435407), a basic igneous rock, possibly of Scottish origin. If natural agents are responsible for emplacing this erratic block, it points directly to ice having overridden these cliffs, perhaps the same ice that deposited the Fremington till. This is by no means the only far-travelled boulder in the district; a whole series has been identified on the coast between Freshwater Gut on the north side of Baggy Point (SS427400) and Saunton Sands (SS445377). These boulders vary in composition, but most imply a northern origin. There is general agreement that they are glacial in origin, although their mode of transport is disputed. Unlike the Baggy Point epidiorite, these erratics are littoral in location, sitting on the shore platforms close to present sea level, prompting the suggestion that they arrived on, or within, grounding icebergs calved from ice-fronts lying to the north or west." (Keene 1996 p 36)
"The largest [erratic], approaching 50 tonnes, is a granulite gneiss somewhat similar in composition to rocks found in western Scotland. This coarse-grained altered granite boulder is located at freshwater Gut (SS 427400)....At Saunton (SS437379) a platform at 5m OD is well-developed. The giant erratic at Freshwater Gut rests on a platform at 7.5m OD. At Pencil Rock (SS423402) a higher platform, at 13.7m OD, notches the sloping cliff." (Keene 1996 p 37) The picture of the Giant Erratic, shown above, is from Photo 11 on p 38.

From a Devon CC web page:

Quaternary
The Saunton-Croyde coast is one of the most important Pleistocene
sites in Southern England. Large erratic boulders sit on wave-cut platforms and are
overlain by raised beach deposits. These erratics are thought to be Scottish in origin,
the most famous being the Saunton Pink Granite (SS 44013787), a gneissose
granitic boulder, weighing some 12 tonnes that might have come from similar
outcrops in Gruinard Bay, Wester Ross. The overlying raised beach deposits consist
mainly of sands with pebble layers and some shingle. Molluscan fauna obtained from
the sands indicates warm or temperate depositional conditions. Overlying these
raised beach deposits are sands of variable thickness which are considered to have
been deposited either in an aqueous environment or to be wind blown aeolian sand.
Stephens (1966) suggests that fossil dune sands were present, whereas Edmonds
et. al. (1979), suggests that marine deposits have been overlain with beach sands
that pass upwards into blown sands containing terrestrial shells. The chronology of
these deposits is disputed, as absolute dating is difficult due to the lack of organic
remains. As the erratics are of presumed Anglian or Wolstonian age (i.e. pre-
Ipswichian glaciation) and the shore platform on which they rest is likely to be of
earlier Pleistocene age. The raised beach deposits are considered to be of
Ipswichian age due to their temperate molluscan fauna.

2 comments:

BRIAN JOHN said...

I hasten to add that it's not me in the photo. Goodness knows who it is -- the photo is an unattributed one, found on some obscure web site. It's very fuzzy because it has been reproduced many times, with fewer and fewer pixels each time.

Myris of Alexandria said...

Were I meddlesome, and I am not, May the Gods forbid,I would use these o say hey the much discussed probable Lewisian Gneiss mace head from Stonehenge,might be an erratic from here picked up and used.
M