Cross-bedding
Wednesday, 26th January 2005
Wild West Yorkshire nature diary
Cross-bedding
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The smaller block (right), about 6 x 6 inches, is pitted with ½ to 1 inch deep holes, like a Swiss cheese. They appear to be in layers but I can't imagine why weathering should have resulted in such a regularly spaced pattern. 12 Months
By the way, if you're interested in the geology of the area, my Yorkshire
Rock - a journey through time, a colourful account of the last 500
million years, is still available and still at the old price of £6.50,
from the British Geological Survey (or through your local
bookshop). Related LinkCountryside Books who publish Village Walks in West Yorkshire Richard Bell, richard@willowisland.co.uk |
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New
Street, Ossett, 9.15 am, cool, overcast
This
weathered face of cross-bedded sandstone reminds me of
Brimham Rocks in the Yorkshire Dales. There a structure like this might
be a gritstone tor 20 feet high but this is a 10 x 6 inch block in a tall
Victorian wall around what is now the health centre in Ossett. The cross
beds represent the layers in a sand bank in one of the rivers that flowed
through this area 300 million years ago, in the Upper Carboniferous
Period. At that time we were on the equator, with dense tropical
forests covering low-lying deltas; a contrast to the damp cool weather
today.
Each
pulse of sediment left coarser particles first, then, as the current ebbed,
progressively finer grains. The grains are now held together by a yellowish
mineral deposit, limonite ('a mixture of similar hydrated
iron oxide minerals', see link below), which acts as a natural
cement. Weathering exploits the varying strengths of the material within
each layer.
I
sometimes get the impression that I'm getting nowhere with my work but
glance at the 'This day last year' link below makes me realise
how much I've done. A year ago I'd almost finished re-walking
my Village Walks in West Yorkshire for the new edition which
is now in print. Since then, in addition to writing up all those walks,
I've published six Sushi Sketchbooks. So I have got somewhere,
despite regular bouts of doubt and despondency.