Category Archives: Geology

All lapis, all, sons!

Lapis Lazuli (Photo ©Tim Jones)
Lapis Lazuli (©Tim Jones)

This is my chunk of Lapis Lazuli: mainly lazurite ((Na,Ca)8(AlSiO4)6(S,SO4,Cl)1-2) with some shiny pyrite (iron sulphide) streaks.  This piece is about 3 inches high.  It’s a semi-precious stone which when ground up becomes ultramarine, the intense blue pigment you see in old religious paintings.  Modern ultramarine is most often synthetic.

Strangely perhaps, my resonance with this rock is poetic, not scientific, as it featured in a Robert Browning poem I studied for my English Literature O-Level; I can still remember sitting in the exam scribbling – all those years ago when dinosaurs still roamed the Earth.

So here it is.  The storyline is about an old Bishop on his death bed, planning the construction of his tomb in a prime spot in the church – something that will outshine that of his predecessor Gandolf (as opposed to Gandalf).  As he rants, the materials of the tomb get grander and grander, progressing from basalt, then basalt embellished with a lump of lapis he has secreted away for the task, to the entire tomb being fashioned from the blue mineral.  All the time he’s getting more and paranoid his family will ignore his wishes and bury him in trashy travertine, gritstone, or, horror of horrors: onion-stone.   Make of it what you will:


“The Bishop Orders His Tomb at Saint Praxed’s Church”

 Vanity, saith the preacher, vanity!
Draw round my bed: is Anselm keeping back?
Nephews — sons mine . . . ah God, I know not! Well —
She, men would have to be your mother once,
Old Gandolf envied me, so fair she was!
What’s done is done, and she is dead beside,
Dead long ago, and I am Bishop since,
And as she died so must we die ourselves,
And thence ye may perceive the world’s a dream.
Life, how and what is it? As here I lie
In this state-chamber, dying by degrees,
Hours and long hours in the dead night, I ask
“Do I live, am I dead?” Peace, peace seems all.
Saint Praxed’s ever was the church for peace;
And so, about this tomb of mine. I fought
With tooth and nail to save my niche, ye know:
— Old Gandolf cozened me, despite my care;
Shrewd was that snatch from out the corner South
He graced his carrion with. God curse the same!
Yet still my niche is not so cramped but thence
One sees the pulpit o’ the epistle-side,
And somewhat of the choir, those silent seats,
And up into the aery dome where live
The angels, and a sunbeam’s sure to lurk;
And I shall fill my slab of basalt there,
And ‘neath my tabernacle take my rest,
With those nine columns round me, two and two,
The odd one at my feet where Anselm stands:
Peach-blossom marble all, the rare, the ripe
As fresh-poured red wine of a mighty pulse.
— Old Gandolf with his paltry onion-stone,
Put me where I may look at him! True peach,
Rosy and flawless: how I earned the prize!
Draw close: that conflagration of my church
— What then? So much was saved if aught were missed!
My sons, ye would not be my death? Go dig
The white-grape vineyard where the oil-press stood,
Drop water gently till the surface sink,
And if ye find . . . Ah God, I know not, I! . . .
Bedded in store of rotten fig-leaves soft,
And corded up in a tight olive-frail,
Some lump, ah God, of ,
Big as a Jew’s head cut off at the nape,
Blue as a vein o’er the Madonna’s breast . . .
Sons, all have I bequeathed you, villas, all,
That brave Frascati villa with its bath,
So, let the blue lump poise between my knees,
Like God the Father’s globe on both his hands
Ye worship in the Jesu Church so gay,
For Gandolf shall not choose but see and burst!
Swift as a weaver’s shuttle fleet our years:
Man goeth to the grave, and where is he?
Did I say basalt for my slab, sons? Black —
‘T was ever antique-black I meant! How else
Shall ye contrast my frieze to come beneath?
The bas-relief in bronze ye promised me,
Those Pans and Nymphs ye wot of, and perchance
Some tripod, thyrsus, with a vase or so,
The Saviour at his sermon on the mount,
Saint Praxed in a glory, and one Pan
Ready to twitch the Nymph’s last garment off,
And Moses with the tables . . . but I know
Ye mark me not! What do they whisper thee,
Child of my bowels, Anselm? Ah, ye hope
To revel down my villas while I gasp
Bricked o’er with beggar’s mouldy travertine
Which Gandolf from his tomb-top chuckles at!
Nay, boys, ye love me — all of jasper, then!
‘T is jasper ye stand pledged to, lest I grieve.
My bath must needs be left behind, alas!
One block, pure green as a pistachio-nut,
There’s plenty jasper somewhere in the world —
And have I not Saint Praxed’s ear to pray
Horses for ye, and brown Greek manuscripts,
And mistresses with great smooth marbly limbs?
— That’s if ye carve my epitaph aright,
Choice Latin, picked phrase, Tully’s every word,
No gaudy ware like Gandolf’s second line —
Tully, my masters? Ulpian serves his need!
And then how I shall lie through centuries,
And hear the blessed mutter of the mass,
And see God made and eaten all day long,
And feel the steady candle-flame, and taste
Good strong thick stupefying incense-smoke!
For as I lie here, hours of the dead night,
Dying in state and by such slow degrees,
I fold my arms as if they clasped a crook,
And stretch my feet forth straight as stone can point,
And let the bedclothes, for a mortcloth, drop
Into great laps and folds of sculptor’s-work:
And as yon tapers dwindle, and strange thoughts
Grow, with a certain humming in my ears,
About the life before I lived this life,
And this life too, popes, cardinals and priests,
Saint Praxed at his sermon on the mount,
Your tall pale mother with her talking eyes,
And new-found agate urns as fresh as day,
And marble’s language, Latin pure, discreet,
— Aha, ELUCESCEBAT quoth our friend?
No Tully, said I, Ulpian at the best!
Evil and brief hath been my pilgrimage.
All lapis, all, sons! Else I give the Pope
My villas! Will ye ever eat my heart?
Ever your eyes were as a lizard’s quick,
They glitter like your mother’s for my soul,
Or ye would heighten my impoverished frieze,
Piece out its starved design, and fill my vase
With grapes, and add a vizor and a Term,
And to the tripod ye would tie a lynx
That in his struggle throws the thyrsus down,
To comfort me on my entablature
Whereon I am to lie till I must ask
“Do I live, am I dead?” There, leave me, there!
For ye have stabbed me with ingratitude
To death — ye wish it — God, ye wish it! Stone —
Gritstone, a-crumble! Clammy squares which sweat
As if the corpse they keep were oozing through —
And no more lapis to delight the world!
Well go! I bless ye. Fewer tapers there,
But in a row: and, going, turn your backs
— Ay, like departing altar-ministrants,
And leave me in my church, the church for peace,
That I may watch at leisure if he leers —
Old Gandolf, at me, from his onion-stone,
As still he envied me, so fair she was!

A Groovy Kind of Rock

Glacier scarred morain rock near Llanberis (Photo:Tim Jones)

A Short Vacation

On a winding stretch of the A5 road from North Wales to London – around Betys-y-coed and Llangollen – mountain scenery combined with the challenge of balancing speed, driver satisfaction, and passenger nausea makes the journey almost enjoyable.  On the other hand, the interminably boring alternations of dual-carriageway and roundabouts that follow – between Oswestry and Shrewsbury – are a recipe for brain death.

Except, that is, one day last week, returning prematurely from a weather-killed ‘Welsh Break’, my mind buzzed over two critical questions the whole trip: What would our broken tent cost to fix?  And why did the grooves on that boulder point to the North East?

Well spotted that woman at the back; this is a post where I obsess about a rock.

Snowdon (Photo:Tim Jones)
Boulder and Snowdon
Location relative to Wales
Location in Wales
Location relative to Llanberis

The boulder in question sits about a half mile down the old Rhyd Ddu road outside Llanberis in Snowdonia.  Its top surface is covered with North East-facing parallel grooves.

And that’s puzzling, because it looks like a moraine boulder dropped by a glacier, in an area where – having walked these valleys for years – I always assumed the ice had flowed towards the North West, away from Snowdon.  Seeing as though the scrape marks left by glaciers – which is almost certainly what these are –  align with the direction of glacial flow, something is amiss.

At this point, lest I raise galactic doubt and uncertainty beyond already dangerous levels, as Douglas Adams might say, rest assured this is all sorted – after a fashion but in a reasonably scientific way –  by the end of the post.  I also got a new tent pole: £15 – thanks for asking.

South Sea Wales

The relevant history starts around 400 million years ago with successive phases of volcanism, weathering, and glaciation (plus some folding and other geological processes).  When the oceanic plate of Iapetus undercut the adjacent tectonic plate of Avalonian – all in the Southern Hemisphere back then – the resulting subduction generated enough heat for volcanoes to punch through Avalonia and form the upland region we now call Snowdonia1.

Source: Wikicommons
Subduction Zone (Source:IAN Symbol Libraries)

The ensuing millenia saw wind, rain, and rivers transform the resulting mountain range from Himalayan grandeur to the more modest heights we see today; yet some of the most dramatic re-modelling was reserved for only the last 20,000 years or so.  And it was caused by ice.

20,000 years ago we were at the peak of a major ice-age that buried the whole region under 1.4 km of ice, with just the tops of the highest mountains poking out.  Moving under gravity, glaciers of rock-bearing ice flowed down the river valleys, gouging out the Llanberis, Nant Ffrancon, and other steep-walled passes, cutting through hard volcanic rock in a series of breaches, and scooping out rounded recesses, or cwms (known as corries in Scotland).

Llanberis Pass on the right, Cwm Brwynog to the left
Llanberis Pass on the right, Cwm Brwynog to the left
View down Llanberis Pass from Llanberis (Photo: Tim Jones)
View down Llanberis Pass from Llanberis

Chunks of rock, liberated by repeated melting and expansion of ice, or plucked out by other rocks, joined the glacier and travelled as an abrasive slurry beneath the ice – scoring anything in their path, before being released as ‘moraine’ when the glacier descended to a warmer altitude or the general climate warmed up sufficiently for the ice to melt.

Boulders falling on the surface of the glacier were likewise dumped, sometimes in incongruous isolation, their angular forms undamaged – like this one just off the Snowdon Ranger Path:

Moraine boulder east of Snowdon near Snowdon Ranger Path / Llyn Ffynnon-y-gwas

A Popular Destination

Glacier-scarred morain rock near Llanberis, North Wales. Photo:Tim Jones
Did Darwin or Huxley pause at this one?

No shortage of historical figures are associated with glaciation and its geographical consequences, including: Louis Agassiz, Charles Lyell, Charles Darwin, Alfred Russel-Wallace, John Tyndall and Thomas Henry Huxley.  Agassiz observed glaciers in Switzerland, and in 1840 was the first to suggest similar processes had operated in the upland areas of Britain (an assertion on which he was closely supported by William Buckland and Charles Lyell.)

Charles Darwin knew the region well2:

“I cannot imagine a more instructive and interesting lesson for any one who wishes (as I did) to learn the effects produced by the passage of glaciers, than to ascend a mountain like one of those south of the upper lake of Llanberis, constituted of the same kind of rock and similarly stratified, from top to bottom. The lower portions consist entirely of convex domes or bosses of naked rock generally smoothed, but with their steep faces often deeply scored in nearly horizontal lines, and with their summits occasionally crowned by perched boulders of foreign rock.”

The glacial boulders of North Wales, with their strange grooving, made a particular impression on Alfred Russel Wallace, the co-discover with Charles Darwin of evolution; commenting in his paper Ice Marks in North Wales3: frequently happens that grooves or scratches are made upon the rocks by the hard materials imbedded in the bottom or sides of the glacier. Owing to the enormous weight and slow motion of glaciers, they move with great steadiness, and thus the markings on rock-surfaces are almost straight lines parallel to each other, and show the direction in which the glacier moved.


Nothing is more striking than to trace for the first time over miles of country these mysterious lines, ruled upon the hardest rocks, and always pointing in the same direction.

Suddenly I feel less alone in my fascination.

In his hugely popular textbook on physical geography – Physiography4 – Thomas Huxley describes how glaciers flow over exposed bedrock to produce characteristic Roches Moutonnees formations (sheep-backs), complete with parallel striations:

Roches Moutonnees, Colorado (from Huxley's Physiography, p.162, 1878)

The Mystery Solved?

But back now to the North West / North East question; a closer look at the Ordnance Survey and Google 3D map projections suggests an answer.

For directly to the South West of our boulder is a more local gouging of the hills in the form of Cwm Dwythwch and its attendant lake – Llyn Dwythwch, suggesting the area was subject to local glaciation running perpendicular to the main ice-flow from Snowdon.  Indeed, the feature is discussed in a paper from the 1950s describing the glaciation as a distinct event, separated from the main ice-flows by 10,000 years in the last period of UK glaciation – the ‘Loch Lomond Advance’.   The cwm certainly aligns with our boulder (pink X marks the spot):

Things are even clearer in glorious Google 3D, North at top:

or looking toward Snowdon:

In Late Glacial Cwm Glaciers in Wales5, Brian Seddon references Cwm Dwythwch and 32 other cwms or cirques in the region arguing they developed from snow and ice preferentially deposited on the sun-sheltered North and North Eastern faces of hillsides, assisted by snow-drifting induced by South Westerly prevailing winds (like we have today).  Seddon recorded the moraine fields of 33 such cirques, plotting their altitude(circles) and aspect(radii) to illustrate the dominance of North/North East facing cwms.  He placed the lowest extent of moraines in the Snowdon Group, containing Cwm Dwythwch, at 275 metres, which is above, but not far off, our boulder’s height at 240 metres.  Maybe he didn’t count every individual boulder at the boundary?  That Snowdonia was formed by a mix of ice-cap and localised glaciation is now widely accepted6,7.

Moraine altitude, aspect, direction in Seddon's Snowdon Group' After Seddon (Ref.5)

All of which, in conclusion, suggests our boulder most likely started life as a volcanic outcrop at the top of Cwm Dwthwch, was carried to its present position by a glacier in a secondary period of low temperatures and glaciation around 10,000 years ago, and picked up abrasions as it was overrun or carried in the North Easterly underflow.

All that with three qualifiers: (a) it’s not 100% certain the boulder is not actually an outcrop of bedrock (need to take a closer look next visit!); in which case it’s fair to assume it was simply overrun by the glacier; and (b) it’s possible the boulder was carried down from Snowdon in the first glacial episode and  subsequently overrun by the secondary glacier (again, more research); or even (c) the boulder  was scarred in the first episode and somehow got spun around 90 degrees just to fool us.

Clearly no rest for the rigorous –  or obsessive weekend geographers – it would seem.

p.s. If any seasoned geologists out there want to put me right / out of my misery, please feel free :-).

Basecamp with pre-broken tent

References / Sources

1. Rock Trails, Snowdonia: A Hillwalker’s Guide to the Geology and Scenery. Gannon, Paul. Pesda Press, 2008

2. Notes on the Effects produced by the Ancient Glaciers of Caernarvonshire, and on the Boulders transported by Floating Ice, Charles Darwin, The Edinburgh New Philosophical Journal, 1842, p.362.

3. Ice Marks in North Wales (With a Sketch of Glacial Theories and Controversies) Alfred Russel Wallace, Quarterly Journal of Science, January 1867

4. Physiography: An Introduction to the Study of Nature. T.H.Huxley, Macmillan, 1878, p.162.

5. Late Glacial Cwm Glaciers in Wales. Brian Seddon, Journal of Glaciology, 1957. In International Glaciological Journal, Volume 3, Issue 22 pp.94-96

6. The last glaciers (Loch Lomond Advance) in Snowdonia, North Wales. Gray JM 1982. Geological. Journal 17: 111-133.

7. Allometric development of glacial cirque form: Geological, relief and regional effects on the cirques of Wales, Ian S. Evans, Geomorphology Issues 3-4, 1986

8. The Early History of Glacial Theory in British Geology. Bert Hansen, Journal of Glaciology, Vol 9, No.55, 1970.

Return to the Land of Charnia

However impressive my best Bear Grylls outdoorsman pose might be, it’s nothing compared to the rocks I’m standing on.

Tim Jones in Swithland Wood, Charnwood Forest
Charnwood Forest
Charnia masoni (Wikicommons)












For this is Leicestershire’s Charnwood Forest, whose +600 million year old outcrops are some of the oldest on the planet. It’s also the area where the very first precambrian macrofossils were discovered by Roger Mason in 1957 (Ref.1).

Before that time, nobody dreamt fossils of this age existed.

And to think I was born only eight miles away in Leicester; gee-whizz.  (The pic above was taken after a family get-together for my birthday a couple of weeks ago. Suspect this was a subliminal attempt to feel younger by standing on something very old.  Can’t say it was entirely successful.)

David Attenborough most recently brought Charnwood and the appropriately named fossil Charnia to popular fame in his 2010 series First Life.  And, as it turns out, he and I  are both Leicester lads who first explored Charnwood as schoolboys.  On which cue I’m handing any further science communication on this ancient world over to Sir David; here he introduces the fern-like Charnia masoni (most relevant part at 2:10 thru 5:50):

And in this piece for Radio 4 he says more about the region, Charnia masoni and its broader implications, plus more on his early fossil-collecting days in Leicestershire:

Bradgate Park, Charnwood Forest (Photo:Tim Jones)


(1) Guide to the Geology of Bradgate Park and Swithland Wood, Charnwood Forest. British Geological Survey, BGS Occasional Report OR/10/041 (pdf is here)

(2) First Life. BBC, 2010

(3) The Story of Charnia and the British Association Festival of Science

(4) A fascinating account of fossil discovery in Charnwood prior to 1957 by Tina Negus at (Thanks Tina Negus)

You might also like on Zoonomian: Attenborough on Darwin
Note: the rocks I’m standing on in the photo are in Charnwood Forest but are not the same outcrop of fossil-bearing rocks in the film