Members Reports and Photos
SATURDAY 25th May 2013
SOILS and FLORA of HOWTH
and Declan Doogue
commenced the field trip by visiting Bottle Quay near where the bedrock geology
of Howth changes from carboniferous to quartzite (Bray Series of Cambrian
origin). The fault line demarking this change extends across the “island” to
Balscadden. Peter gave an overview of the geology of Howth in the context of
Dublin Bay, the Wicklow and Dublin Mountains and paid particular attention to
last glacial period (Ice Age). He pointed out to us the striations on the rocks
next the cliffs which are evidence of the movement of ice and this was also
visible within the ‘erratics’ in the exposed glacial till on the cliffs
above the beach.
moved on to Balscadden Bay and viewed the local geology and noted the rather
precarious military position of the Martello tower built on consolidated delta
sand which at one time stretched across to Kilrock. Peter expounded on our
glacial history and on the evidence for changes in the earth’s climate due to
the Milkankovitchian cyclical alterations to the earth’s attitude and
movements relative to the sun. Inevitably the discussion turned to carbon
dioxide levels in the earth’s atmosphere which have recently breached the 400
ppm mark, and to sea levels and future climate …. A little bit of beach
combing uncovered some rounded Ailsa Craig granite which had been brought by the
ice sheet when moving down the Irish Sea.
Red Rock quarries we looked at the Variegated Horsetail Equisetum
variegatum – a lime loving plant – and pondered the pH of seepage at the
bottom of the cliffs which are composed of acid rock. What mysterious path is
followed by the emerging water?
was a superb and very informative field trip. Copies of Wicklow
in the grip of an ice age (Peter Coxon, Fraser Mitchell and Patrick Wyse
Jackson), published by the Irish
Quaternary Association are obtainable from http://www.iqua.ie/.
This publication covers much of Peter’s talk and