On Wednesday afternoon we drove across to Troon, travelling via Moffat so that we could visit the Ordovician-Silurian GSSP at Dob’s Linn (55.4400°N 3.2700°W according to the SSI). The region is a truly lovely glaciated landscape, with U-shaped valleys, hanging valleys, waterfalls etc. The area to the west of Dob’s Linn is a National Trust for Scotland Nature Reserve – Gray Mare’s Tail. A 60m waterfall falls down the side of the main valley, and walks lead up to the top of the waterfall to Loch Skeen (a corrie loch). It’s a lovely walk, and is a delightful example of textbook glaciated landforms (including a kettle hole hidden off to the right of the path just before the loch). The area is also of great ornithological interest thanks to its peregrine falcons, ring ouzel(s) (not sure how to pluralise that) and black grouse. It’s a delightful walk up there – unfortunately we didn’t have time to do the whole thing on this particular occasion, so we simply parked at Dob’s Linn. I previously went up there as part of a joint Advanced Higher Geography/Biology field trip in high school.
Anyway, back to our little excursion. We parked the car at the inconspicuous parking spot next to Dob’s Linn (the little valley is almost completely unsignposted or marked in any way – probably to help preserve it).
Dob's Linn from the road
We wandered up through the valley, finding the occasional graptolite rich fragment amongst the large scree slopes of black shale. Turning left we climbed up the Linn branch (a warning to people wanting to follow us, this involves clambering round some steep scree slopes – it’s not the safest excursion for the young or infirm and is extremely unwise to do alone). This branch of the gorge is really quite lovely, both geologically and aesthetically:
Some lovely, slightly folded shales to the South side of the branch
Ripple Marks (I've cheated here, this is a photo from a prior visit)
The Waterfall at the End of the Branch
That waterfall was particularly lovely last time I visited the area, in the deepest darkest Scottish Winter:
Frozen Waterfall
There are two excavated areas in Dob’s Linn: the Linn trench and the North trench. Both of these trenches show large sections of the strata, which have been examined and catalogued in detail by Lapworth and later Williams. Time didn’t allow us the opportunity to examine the North trench, however we were able to see the Linn branch trench, and examine the scree slope below it – within which many Graptolite specimens could be found.
The Linn Branch Trench
This photograph covers the border between the Ordovician (from where the photograph was taken) and the Silurian (where Hazel is sitting). Somewhere between us (I can’t put my finger on exactly where) is the FAD of Akidograptus Ascensus – the acknowledged boundary or ‘golden spike’.
After this we clambered back down and drove west to Moffat then back up the west coast. It’s worth noting that there are a great deal of excellent examples of slope failure along the road to Moffat (this area would make a fantastic day trip for a geography or geology class).
Following are a number of photographs of samples obtained from the loose scree material:
Some small fragmented graptolites - few specimens are preserved completely intact
More Examples
Not entirely sure what these are - any suggestions?
Layer of pyrite within the shale
These shales are really lovely, you can pull apart layers with your hands to reveal a new layer filled with graptolites or, as above, pyrite.
Tags: Borders09, Geology, Ordovician, Quaternary, Silurian