| Dear Alan I
have just read and enjoyed your article in the last issue
of The Edinburgh Geologist about 'Red Rocks' and would like to add some of
my own observations... On field courses to Skye and Mull I have used names to
help students identify the location of acid and basic Tertiary outcrops. On Mull
I use Riadh Sgeir (602247 - granophyre) and Rubha Dubh (570213 - basalt), both
near Lochbuie as examples. On Skye, Meall Dearg (4923) distinguishes a patch of
red Meall Dearg Granite from the surrounding basic rocks of the Black Cuillin'.
My letter concerns Mull... you suggest that 'there
is a paucity of red place names' on the island. Certainly they are not numerous,
but I am aware of 23 on Mull and surrounding islands (including the ones that
you have already identified):
1. | Aird
Dearg | 463390 | Tertiary
basalt | 2. | An
Geodha Dearg | 260230 | Lewisian
amphibolite and iron bands | 3. | Boghachan
Ruadha | 422342 | Permo-trias
conglomerate/ breccia | 4. | Bogha
Ruadh | 298428 | Tertiary
basalt | 5. | Cadha
Ruadh | 423243 | Tertiary
basalt | 6. | Cruachan
Dearg | 568332 | Tertiary
basalt | 7. | Dearg
Bhealach | 475199 | Tertiary
basalt | 8. | Dearg
Phort | 305251 | Silurian
Ross of Mull granite | 9. | Dearg
Sgeir | 294156 | Silurian
Ross of Mull granite | 10. | Dearg
Sgeir | 405268 | Tertiary
basalt | 11. | Dearg
Sgeir | 595453 | Tertiary
basalt | 12. | Eilean
an Ruadhaidh | 491257 | Tertiary
basalt | 13. | Lochan
Dearg | 488508 | Tertiary
basalt | 14. | Red
Rocks | 530591 | ?
(not identified on geological map) | 15. | Ruadh
Sgeir | 308149 | Silurian
Ross of Mull granite | 16. | Ruadh
Sgeir | 602247 | Tertiary
granophyre | 17. | Sgeir
Dhearg | 406547 | Tertiary
basalt | 18. | Sgeir
Ruadh | 276223 | Silurian
Ross of Mull granite | 19. | Sgeir
Ruadh | 434411 | Tertiary
basalt | 20. | Sgeir
Ruadh | 732362 | Tertiary
craignurite | 21. | Sgiath
Ruadh | 565447 | Tertiary
basalt | 22. | Sgriob-ruadh | 493550 | Tertiary
basalt | 23. | Sgurr
Dearg | 665340 | Tertiary
volcanic breccia | No.
2, from Iona, introduces rocks of an age not mentioned in your article - the Lewisian.
The map published by the Iona Community shows the name An Geodha Dearg and also
indicates that the rock is Lewiaian amphibolite with iron-rich bands [geodha translates
as a creek or coveformed by surrounding rocks]. You
suggest that the 'Ross of Mull is lacking in red place names despite being
granitic'. In fact at least one 'red' name does exist, no. 8 on my list Dearg
Phort, just north of Fionnphort (352251) [Fionnphort translates as white harbour
and Dearg Phort as red harbour]. In addition, there is no. 18, Sgeir Dearg, which
lies just off the coast of Iona, but which is also formed from the Ross of Mull
granite. (This is another example I use with my students as it shows that the
fault which runs through the Sound of Iona, possibly a continuation of the Moine
Thrust, must lie very close to the east coast of Iona). Mull
also provides an example, no. 3, from the 'just about hopeless' New Red Sandstone.
Off the coast of Gribun is the rocky outcrop of Boghachan Ruadha which, according
to the new Staffa geological map, is formed of Permo-triassic conglomerates and
basal breccia. What is perhaps most surprising
about Mull, however, is that over half (13) of the 'red' place names are actually
found where the bedrock is basic basalt and would be expected to be black. Presumably
this is due to weathering either in the Tertiary (producing bole), or more recently,
oxidising the iron. Yours sincerely Ian
Winterflood
Geology Department, Arnold School,
Blackpool.
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