Dear Readers, it felt very strange to wake up this morning and realise that I had actually managed to get everything done that I wanted to get done yesterday, but I didn’t have long to cogitate as we had an organised Geology walk in Coldfall Wood today. It was on the subject of geology, which for me is the unheralded crux of ecology – what underlies the soil determines so many things, from the soil organisms that will thrive to the plants that will grow, as anyone who has tried growing chalk-loving flowers in a London clay garden will tell you. The walk was led by Diana Clements, who is currently revising her book ‘Geology of London’, which is well worth a look for anyone even vaguely interested in the deep history of our area.

We looked at the main rock types in the area – London clay, Dollis Hill gravel and glacial till. Diana’s walk rather cleverly takes us through the three stages of the history of the wood as reflected in their geological history, and I for one will never look at the them in quite the same way again.

The rather unprepossessing bit of the stream above shows that the banks are London clay, and Diana had a box full of fossils found in clay, from North London molluscs, shark’s teeth, palm seeds and magnolia seeds. The clay was first laid down about 50 million years ago, when the climate was probably tropical (though the magnolia seeds may suggest at least some seasonality). Magnolias are ancient flowering plants that are pollinated by beetles, as there were no specialist pollinators about at the time.

Next it was off to the wet woodland for a look at the Dollis Hill gravel. The Thames used to run to the north of London, through the Vale of St Albans and then into the North Sea at Clacton, until it was diverted by the glaciers of the Ice Age. Some of its tributaries flowed through what’s now Coldfall Wood, depositing gravel as it went. You can find all sorts of interesting things in gravel, including quartz and the flinty Lower Greensand Chert.

The bed of the stream into the wetland area is full of gravel.

And finally, there’s the glacial till. One finger of the last glacier of the Ice Age (which retreated about 400,000 years ago) reached as far south as Coldfall Wood (and also Hornchurch in Essex for anyone who lives in those parts). As it retreated it ‘dropped’ all the rock fragments that it was carrying (to a depth of 14 metres in Finchley), and simultaneously excised deep gullies as the water in the ice sheet melted, while the surrounding soil rebounded after being compressed by the ice. No wonder the woods are so undulating, although they’re probably less so than they used to be, as the London Clay is a very soft material, easily eroded.

So, it was a fascinating walk, and I seem to have retained rather more of it than I thought I had at the time. I will certainly look at the woods in a new light!

And for those of you who read my piece on Crape Myrtle last week, I stopped to check out the bark on the tree and it is indeed both rather attractive and very smooth. What amused me no end is that having noticed one small tree, I completely failed to notice that there was another Crape Myrtle next to it. It just goes to show how distracted I’ve been, but no longer!

Crape Myrtle bark

Dear Readers, as you might remember I was in Coldfall Wood yesterday for our spider walk, and a lot of fun it was too. Well, between midday on Saturday and first thing this morning, one of the dead standing trees alongside the boardwalk has toppled over and smashed part of the bridge.

For once, it’s very unlikely that this was caused by vandalism – it’s too far from the boardwalk for someone to pull, and it’s completely surrounded by stinging nettles so it’s unlikely that someone would have waded through them to give it a push. Standing deadwood is normally pretty stable, so what could have caused the problem? I have a  theory, so here goes.

First up, the area here in Coldfall is a habitat known as wet woodland, which is extremely rare, especially in urban areas. Water runs down into the area from a variety of culverted streams, and also seeps in from the higher ground that surrounds it. In the winter the area has, in the past, been flooded to a depth higher than the handrails, and the photos below give an idea of what it’s often like in a normal and exceptionally wet winter.

A normal winter

An exceptional winter (Photo courtesy of Neville Young from 2020)

However. In recent years, there have been some attempts to improve drainage – for one thing, one of the pipes that took excess water away was forever getting blocked, so the water backed up. This was then cleared.  But I am now a little concerned that the ‘wetlands’ is getting too dry – where there used to be water mint and water bistort, there’s now a sea of stinging nettles. Clearly, you can have too much of a good thing  where drainage is concerned, because the last thing  we need is for the wet woodland area to dry up altogether.

Naturally, the amount of water in the wet woodland is to a certain extent weather-dependent (and it has been a pretty dry summer), but I have never seen it this dry in late summer.

Water mint and water plantain in the wet woodland from 2014

Water Plantain, amphibious bistort and bulrushes from 2020

Now, of course a dead tree can topple over at any old time. However, I suspect that the  the weather (hotter than usual for this time of year) and the dryness (as evidenced by the changing vegetation) are contributing and helping to destabilise the soil.  We really do need to sort out the drainage issue here, before we lose this precious and unusual habitat for good.

You can read a bit more about the different kinds of wet woodland, and its value to wildlife, here.

Dear Readers, I am still in the throes of year end but am determined to get out for a quick walk at lunchtime – there’s always something to see, and even old familiar sights, like All Saints here on Durham Road, look all the lovelier against a colour-washed blue sky. I dragged my husband across the road to examine the bulbs, and some of the daffodils are almost in flower already.

And then there’s the fact that all the bollards are upright, as opposed to reclining drunkenly to the horizontal having been backed into by a passing van.

And I rather think that this tree is an alder, though it isn’t marked as such on the London Tree Map. I could of course be wrong though – I’ll have to have a closer look next time I whizz past.

In sad news, the tree that was walloped and damaged when a skip was being loaded a year or so back has finally been cut down. It sustained a huge wound and as it wasn’t treated, the trunk started to rot.

The crab apple originally

Following the encounter with the skip

Today

It’s always a shame when a mature tree is cut down, especially when I suspect that if it had not been damaged, the crab apple would have survived for many more years. But accidents happen, our road is narrow and tricky to manoeuvre around, and everyone is under such pressure these days. And clearly you can’t have branches descending onto the noggins of innocent passersby. Plus, the street has received half a dozen new trees this year – although they’re just saplings at the moment, hopefully they’ll have a chance to mature and grow into fine specimens.

But, to end on a more cheerful note, I cannot pass this row of houses on Lincoln Road without smiling.

Each one has a presiding spirit above the doorway. There’s a very sad Poseidon…

..a chap with a very fine moustache…

and this lady, whose rather serious demeanour is offset by that splendid lipstick. I can just imagine someone standing on a stepladder, determined to give her a suitable starlet makeover.

And then, finally, I loved these rowan berries against the moss. It looks like game of bowls played by some mice.

And now, suitably buoyed up, it’s back to the spreadsheets. And goodness, it’s almost February! Soon year end will be over, and I’ll be able to get back to some sort of normality.