WALK LONDON Green Chain Walk - GEOTRAIL[sections 5, 4 & 2] Thames Barrier to Lesnes Abbey (7 miles)
The Green Chain is a collection of footpath filaments that spread out across southeast London from Erith to Crystal Palace. This Geotrail links several segments together, connecting a dozen points of geological interest through Charlton, Plumstead and Abbey Wood. All you need is the leaflet - short version here, more academic version here. It's an unexpectedly fascinating stroll, especially if you've not been this way before.
The Thames Barrier's not there by accident, you know. All those heavy gates need support, which is provided by a narrow ridge of chalk cutting beneath the river [photo]. To find out more you could explore the exhibition at the Visitor Centre, although it's so brilliantly disguised as a cafe you'd probably never guess the basement attraction was there. Just inside the main door you can also pick up the free Geotrail leaflet - they appear to have dozens left, because I guess it's hard to persuade visitors just arrived by car that walking to Thamesmead is a good idea. Rest assured, it is a good idea.
On heading inland you'll reach Maryon Park where at a signpost the path divides. Absolutely definitely turn right, unless you're on wheels, to climb steadily to the top of Cox's Mount. The view from the summit is undoubtedly best in leaf-free midwinter, but all year round the panorama includes Docklands, Dome and Dangleway, plus London's great river meandering through [photo]. This is the final hill on the downstream Thames, with a former quarry beyond in which the strata of geological time are revealed. An information board at Gilbert'sPit explains all, in refreshingly non-dumbed-down language - rarely in London are layers of sand and clay exposed as clearly as this.
At Charlton Park, past an enclosure of cute deer, the walk turns east along the escarpment and keeps going. The walk crosses Woolwich Common, where normally the grand Georgian barracks are the main point of interest, but not this summer. The aliens have landed, in the form of a white cuboid with fluorescent nodules which forms the heart of the London 2012 Shooting venue. It's wildly out of place, surrounded by a tented village and emerging grandstands, but undeniablyeye-catching. In a couple of weeks Ha-Ha Road will be sealed off to traffic, for the Games, with Green Chain walkers diverted round to the south. That's closer to Shooters Hill, which the trail guide points out is one of the few remaining areas of non-eroded London Clay south of the river. But you'll still be staring at the Teletubby village down the hill, I guarantee. [photo]
The yomp across the top of Woolwich isn't lovely - someone let a bunch of 70s architects loose south of Nightingale Place and the end result isn'tpretty. But soon comes Plumstead Common, and a linear mile or two of green, just too far back for a decent view down across the Thames. I missed the Dog Rocks, two chunks of canine-shaped pebbledash supposedly hidden in a shrubbery by the adventure playground. But I easily spotted Plumstead's former windmill, long since sail-less, now a pub [photo]. And I was amazed by The Slade, which is a wholly unexpected gorge created long ago by torrents of water. Landslips helped create a deepnotch - a ravine in suburbia - its slopes now covered with thick woodland. At the bottom, umpteen steps down, is a dark pool watched over by three scowling teenage harpies. If you're lucky they won't be here when you visit, but I didn't hang around.
Winn's Common is more extensive, more open, with the occasional glimpse of Barking across the chimneytops [photo]. Close by are the brickfields that helped to create housing over this corner of London, made easier by a fortunate coincidence of clay, sand and pebbles. You can see these Blackheath Pebbles underfoot in Bostall Woods, on the next hill along, across a lost river valley. The woods are in complete contrast to the urban nature of the walk thus far, completely secluded, remarkably peaceful, with barely another walker in sight. The Bostall Heath bowling green provided a brief outpost of civilisation, its members resplendent in Daz-perfect whites. Then it was back into the trees, past hidden ponds, to almost the end of the walk.
The Geotrail diverts off the Green Chain right near the end, to climb a long steep slope within Lesnes Abbey Woods. The given reason is to see Chalky Dell - a romantic name for what turned out to be a small deep quarry dug deep into the sand by monks. It's overgrown and missable. But on the final path, in an enclosure just off to the left, is the must-see Fossil Bed. It was discovered by a geologist walking his dog in the 1870s, who found shells and sharks teeth and later the bones of an unexpectedly high number of small mammals. It's one of the richest 55-million-year old sites in the world, and Bexley Council forbids excessive digging without a permit. But poking around on the surface is OK, so long as no more than 2kg of soil is removed, and you might (like me) walk away with an unidentified fossilised incisor.
The stones beyond the treeline aren't natural, they're all that remains of medieval LesnesAbbey[photo]. Although more than a mile from the river, this is the first spot where the land rises above the floodplain, and is rather safer from inundation than the Thamesmead estate below. The Green Chain continues along a concrete walkway all the way to the Thames, but the Geotrail halts here. If you fancy a walk that's a bit different, with a little scientific rigour thrown in, thisrocks.