Cycling UK Forum

Jon Lucas wrote:If it is raining, head to Anglesey. When we are there, we often watch the rain throwing itself down over Snowdonia while we bask in sunshine.

Interestingly (for me at least) Anglesey is different in another way. Geologically. Whereas the rest of Wales is one geological mass, built up over millions of years, Anglesey is a separate body that has slid in alongside the main body of Wales. The Menai Strait is the fault line.

That's not quite correct.

Angelsey is (for the most part but not only) Precambrian - a Precambrian plain.
The mountain mass of of Snowdonia and beyond,is a large (pretty much) unbroken sequence of ancient sedimentary rocks laid down upon that Precambrian base.
The oldest part (and largest) of that sedimentary sequence are the Cambrian sediments of the Harlech Dome (with some outliers nearer to Angelsey) which was proven in the Brynteg Borehole to lie upon a Precambrian base.

A quick Google produced this about Brynteg,
but BGS would have more, it's fascinating stuff, (no pun intended!).
http://earthwise.bgs.ac.uk/index.php/Co ... ian,_Wales

Re. the OP- its damp but very mild with only occasional rain probably drier and even milder to the East of high ground. Little wind.
Nice enough on a bike for sure at the moment.
In fact it's brightening up!!

PDQ Mobile wrote:That's not quite correct.

Angelsey is (for the most part but not only) Precambrian - a Precambrian plain.
The mountain mass of of Snowdonia and beyond,is a large (pretty much) unbroken sequence of ancient sedimentary rocks laid down upon that Precambrian base.
The oldest part (and largest) of that sedimentary sequence are the Cambrian sediments of the Harlech Dome (with some outliers nearer to Angelsey) which was proven in the Brynteg Borehole to lie upon a Precambrian base.

A quick Google produced this about Brynteg,
but BGS would have more, it's fascinating stuff, (no pun intended!).
http://earthwise.bgs.ac.uk/index.php/Co ... ian,_Wales

Re. the OP- its damp but very mild with only occasional rain probably drier and even milder to the East of high ground. Little wind.
Nice enough on a bike for sure at the moment.
In fact it's brightening up!!

My understanding, from listening to a lecture give by a geology professor, was that Anglesey was moving NE and at one time was not joined to Wales at all.

My understanding is that the similar ancient geology of North Wales, including Anglesey changed when several volcanoes heaved up ash and lava, 450 million years ago becoming the still-changing Snowdonia range. Anglesey missed those, except for ash although it has schists, dykes etc and so is generally flatter, made more flat by the ravages of over 20 ice ages that resulted in icesheets pressing down on it rather than glaciers eroding the valleys as in Snowdonia.

As a former geography teacher I took many field trips all over that area. One year a geology teacher came with us and for a week his students did nothing but study the greywacke rocks in Aberystwyth. A whole week of examining a grey sandstone! At least I knew there was such a thing as greywacke by the end. LOL. And I noted the Aber uni students mostly had extra big derailleurs to cope with the slopes.

pwa wrote:My understanding, from listening to a lecture give by a geology professor, was that Anglesey was moving NE and at one time was not joined to Wales at all.

The broad structure of Snowdonia is synclinal.
That is it is the bottom of a large fold.
The summit of Snowdon shows this clearly towards Glaslyn.
Marine fossils can be found just under the summit.


These massively thick sediments have been almost unbelievably eroded. Given that Snowdon was at the bottom of a geological "valley" it seems likely that the sides of that valley swept upwards and over Angelsey. Because anticlinal structures are more heavily faulted they are eroded far more quickly especially by ice.
Anglesey was subject to massive glacial scouring though several iceages.

It would seem pretty certain that Angelsey given its proximity to the Snowdon massive was at one time covered by those sediments,which have now disappeared.

Menai is but one of several large but ancient faults surrounding the area. Its presence probably weakened the the anticlinal sediments on Anglesey even further.

All IMHO.

PDQ Mobile wrote:

pwa wrote:My understanding, from listening to a lecture give by a geology professor, was that Anglesey was moving NE and at one time was not joined to Wales at all.

The broad structure of Snowdonia is synclinal.
That is it is the bottom of a large fold.
The summit of Snowdon shows this clearly towards Glaslyn.
Marine fossils can be found just under the summit.


These massively thick sediments have been almost unbelievably eroded. Given that Snowdon was at the bottom of a geological "valley" it seems likely that the sides of that valley swept upwards and over Angelsey. Because anticlinal structures are more heavily faulted they are eroded far more quickly especially by ice.
Anglesey was subject to massive glacial scouring though several iceages.

It would seem pretty certain that Angelsey given its proximity to the Snowdon massive was at one time covered by those sediments,which have now disappeared.

Menai is but one of several large but ancient faults surrounding the area. Its presence probably weakened the the anticlinal sediments on Anglesey even further.

All IMHO.

A quick search has led me to the suggestion that Anglesey docked with the adjacent mainland in or about the late Pre-Cambrian, which is a long time ago even in geological terms. So it was more or less fused to the rest of Wales since then, experiencing the same geological history thereafter.

Yes that is my understanding of it.
Sorry I am so long winded.

PDQ Mobile wrote:Yes that is my understanding of it.
Sorry I am so long winded.

And all unlikely to affect the OP's cycling experience in the next few days.

Ah. actually I have found a laymans interest in the geology of places an interesting facit to any journey.

I might add -"especially along the N. Wales coast!!!"
Let us wish him dry weather and light winds.

The views of Eryri from Ynys Mon are better than the close-up views, one does not have to crick ones neck. Two weeks on the north Welsh Riviera this year, almost no rain but some beautiful snow above 500 m.

I should have reported back earlier. That short excursion to Betws-y-Coed earlier this month was marvelous. Temperatures around 8 C is okay when working hard in the hilly North Wales and when the sun did peep through, the views were stunning. This about 6 miles from Cerrigydrudion towards Ruthin.

Amazing photo.

Cyril Haearn wrote:The views of Eryri from Ynys Mon are better than the close-up views, one does not have to crick ones neck. Two weeks on the north Welsh Riviera this year, almost no rain but some beautiful snow above 500 m.

One of the most delightful things about cycling in Ynys Mon (Anglesey) are the views over the Menai Strait to the full range of Snowdonia's mountains. The combination of very quiet lanes, staggeringly beautiful countryside and stunning views, puts a few of the island's lanes into my top cycling roads for pottering round in this country.

Jon Lucas wrote:

Cyril Haearn wrote:The views of Eryri from Ynys Mon are better than the close-up views, one does not have to crick ones neck. Two weeks on the north Welsh Riviera this year, almost no rain but some beautiful snow above 500 m.

One of the most delightful things about cycling in Ynys Mon (Anglesey) are the views over the Menai Strait to the full range of Snowdonia's mountains. The combination of very quiet lanes, staggeringly beautiful countryside and stunning views, puts a few of the island's lanes into my top cycling roads for pottering round in this country.

Yes Wales without the big hills and with fascinating history. There was a great programme on S4C about historic field names on Ynys Mon.

Just don't tell too many people about it.

Cymru am byth!

Geoff_N

It's good to hear it went well.