Is Anglesey the most geologically diverse 710km2 in our Solar System? Rob Crossley GeoMôn

Rob Crossley from GeoMôn gave this catchily-titled talk to Mid Wales Geology Club members in Newtown and elsewhere via Zoom on 19th June 2024. Rob started off by telling us of his international geological experience which started off with a PhD thesis in the East African Rift Valley. He then moved on to what we know about geological events in several other moons and planets of our solar system. Obviously we don’t know much, but we have seen evidence of lava flows and water channels which took place in the distant past. There does not, however, seem to be anything like the range of geological appearance we see here on Earth.
Rob moved on to the diversity of the geology within Ynys Môn, and how it had been captured on previous maps, starting with Williams Smith’s 1815 map. Then on to John Henslow’s map published in 1822, in which he managed a very detailed and accurate map after just one summer of exploration. Finally we had the Greenly’s map of 1919, which is virtually the same as current BGS maps. Edward Greenly introduced the term mélange to geology with his description of the Gwna mélange.
In the latter part of his talk, Rob illustrated the wide range of geodiversity within the island starting with the last Ice Age and then working back through various geological periods to the late Precambrian. At the end of the talk, the audience were happy to answer the question in the title with a resounding YES.

Part of the Gwna melange seen near the Wylfa nuclear power station. This exact location had been accurately sketched and annotated by John Henslow in 1821 with the large block of pale quartzite centre left and the dyke intruding near the bottom right.

The northern side of the Menai Straits at Lleiniog. The best example of a sub-glacial tunnel valley in the UK

A closer view of the above shows small fragments of coal trapped within the material.

The following two photos depict pillow lavas on Llanddwyn Island. Speaker used for scale in first photo.

Closer view of the pillow lavas

Text and photos by Dr. Chris Simpson MWGC