Richard Bell's Wild West Yorkshire nature diary, Tuesday, 24th July, 2007
THIS SANDSTONE fragment and pebble, which I picked up from a flower bed at Barbara's mum's, are the bedrock of the small town of Horbury, in fact this particular bed of sandstone is known as the Horbury Rock and is made up of fine grains of sand from a delta which stretched from here north to the M1/M62 junction near Lofthouse, east beyond Castleford and to the south-east as far as Upton; an area of at least 10 x 25 kilometres (6 x 15 miles).
Not that there were towns and motorways at the time; you'd have needed a canoe to explore the tropical lagoons and backwaters of the river. Dragonflies the size of sea-gulls whirred about, huge cockroaches and centipedes trundled through the undergrowth and giant newt-like amphibians the size of crocodiles hauled themselves out into the lush forests of giant club-mosses and horse-tails.
300 million years ago, in the latter half of the Carboniferous period, grey mudstones, coal and sandstone were deposited in lagoons, swamps and river deltas when our part of the world lay close to the equator. The Horbury Rock delta probably stretched a bit further but the bed of sandstone has been eroded away at its exposed side and is hidden where it dips under younger rocks.
Drawing rocks and pebbles is like drawing a miniature landscape which you can hold in your hand. The facets, snaking cracks and ridges, particularly when viewed through a hand lens, remind me of the cliffs, channels and canyons of a planet or asteroid, as seen by space probes. I try to draw as accurately as I would if I were mission artist on an interplanetary probe.
What colour is this sandstone? My starting point is yellow ochre but with touches of practically every other colour in my small watercolour box added to dull it down and modulate it, including touches of raw umber and Payne's grey. A fresh fragment of Horbury Rock would be more the sandy colour that you might expect but these fragments have been weathered, oxidised and no doubt have microscopic colonies of algae and bacteria adding to their patina.