A Geological Walk Round Ruthin

In 1831Charles Darwin, an English naturalist, geologist and author of the book 'On The Origins Of Species,' had recently passed his BA exams with honours, and in August that year he accompanied his geology tutor, Professor Adam Sedgwick, on a two week field trip to map the strata of Wales. On the journey up from Cambridge they stopped off in Ruthin and reputedly stayed in the Castle Hotel on St. Peter's Square. Charles and Adam parted company at Bangor, leaving Charles free to explore the rocks of Snowdonia. While in Cwm Idwal he identified igneous rock and fossil corals. Last year Berwyn District and Ruthin District Geology Group U3A's had a field trip to Cwym Idwal guided by Paul Gannon, mountaineer guide and science technology journalist following in Charles Darwin's footsteps. I would like to think that during Darwin's stay he saw some of the town's geology in the old building materials and structures around Ruthin Town. Last year in October, our U3A Geology Group too geological walk around Ruthin. We were guided by group member Brian Hubble who not only gave us a splendid fact filled tour but also produced a two-page hand-out. In any town or village, you can get an idea of the local geology just by looking at the materials used in the old buildings as it was so much cheaper to use local stone. Our first stop was Bathafarn Chapel which has 300 million years old yellow sandstone around

windows and porch. It may have been quarried around Ruabon which is known for its Cefn y Fedw rock. In the walls of the County Hall we saw belemnites and brachiopods fossils in the 300 million year old carboniferous limestone. The splendid pillars are of the igneous rock Larvik. It was probably quarried in the Larvik mines in Norway. You can see thumbnail size crystals of feldspar quite easily The War Memorial which is constructed of three types of rock. The grey metamorphic Ordovician slate found in the Ffestiniog and the Dee Valley region. Permian Triassic sedimentary sandstone found in Hirwaen and Cheshire and igneous granite which may have been mined in Cornwall. Ruthin or Denbigh quarries could have supplied the carboniferous limestone which contains easy to see calcite tubular corals and circular fossils that was used to build the Town Hall A great sight is the kerbstones around St. Peter's Square which are made of crinoidal limestone. Crinoids were around in the Ordovician era about 488 million years ago. The fossils we see are the broken stems of the marine animals and look like miniature polo mints. This limestone may have been mined around the Matlock area. The Old Gaol's carboniferous building blocks contains brachiopod fossils and the Tom Price Memorial has a slate plinth probably from a Berwyn quarry and the main stone is a type of limestone, a very hard dolomite, which could be Permian from 200 million years ago. Another very curious and interesting feature is Maen Huail, the large stone outside the Midland Bank. It is thought to be an erratic. Erratics are stones that got wedged under moving ice during the various ice ages. When the last ice melted 14,000 years ago, stones were left behind on completely different geological formations. There is an enormous erratic Maen Digychwyn in Eryrys village now used as part of a garden wall and is well worth viewing.

In March 2017, ISABEL STEWART guided us through some of the town’s rocks and fossils