It may be 50 million years too late to go for a sea dip in Hertfordshire, but do make an online date with the postponed Gerald Salisbury Memorial Lecture when chalk landscape expert Haydon Bailey will talk about the county's fascinating geological history (8pm on Wednesday 23 February

Dr Bailey is Chair of Hertfordshire Geological Society and a stratigraphy expert who also lectures at Birmingham University. His lecture will consider what it would have been like in Hertfordshire a hundred million years ago and how it has changed over significant periods in geological time.  He will describe the formation  of the county's chalk scenery and the impact of the Ice Age on its landscape and natural history.

The Zoom link for the lecture is  https://us06web.zoom.us/j/82324600844 (Meeting ID: 823 2460 0844). Members and guests will be able to join from 7.45pm in time for a prompt start.

Questions Haydon plans to address include  'How deep was the Chalk Sea (and how warm was it when you went for a quick swim)?' , 'Who or what made the Hertfordshire Puddingstone?' (see photo, ©Jack Fearnside)  and 'Where was Hertfordshire's coastline in the Eocene period and what was living there?'.

He will also bring the 100 million year story up to date by considering the implications of climate change for the Chiltern region and even – time permitting – the impact of the HS2 railway line.

The Gerald Salisbury Memorial Lecture is organised jointly by the Welwyn Natural History Society and Hertfordshire Natural History Society and normally takes place in November. It had been hoped to hold the lecture at Welwyn Civic Centre. However, uncertainty concerning the continuing Covid outbreak has led to a decision to hold the lecture online.