On Saturday 21st May
around eighty people came to Thurstaston for a guided geology walk presented by
Hilary Davies of Liverpool Geological Society.
She provided a fascinating overview of
the impact of glaciation on the Dee and Mersey Estuaries and explained how the
ice sheets, when coming south, had been diverted eastward by the Welsh
Mountains and had carved deep valleys as they moved inland. Apart from
the visible sandstone outcrops in Wirral such as Thurstaston Hill the rest
of the Peninsular is covered by glacial deposits of boulder clay – now called
till. It is impermeable and so enables water courses to exist, such as
the Arrowe Brook, Birkett, Dibbinsdale Brook and Fender.
We next walked along the beach and
collected specimens of rock which were given to Hilary for comment. She
detailed their individual geological age and history as igneous, metamorphic or
sedimentary and told us of the locations from which the glacier had collected
them, some from N.W. Scotland. Some samples demonstrated striation in
which they had been scraped along rock whilst being gripped in the ice. Others showed where rock had been stressed and fractured allowing other
quartz and minerals to enter in water and later to solidify. Even the rock
armour forming the new sea defences below Dee Sailing Club revealed remarkable
minerals and fossils and gave insight into the geology of
North Wales from whence they had come.
We were treated to an inspirational
presentation delivered with great clarity and detailed explanations and all in
fine weather.
Stephen Ross
