Nodular Limestone with bentonite layer

Image: © Rudi Winter Taken: 8 Jun 2014

At a quarry on the west side of Wren's Nest, a good insight can be had into the internal structure of the Nodular Limestone Member. Here thicker limestone layers alternate with thin bands of sandstone. The limestone is a deposit from shelly organisms living in a shallow shelf sea, while the sandstone is terrigenous, i.e. has been transported here by rivers after flooding events on nearby land. Amongst this, there are two thin and very crumbly layers. These are made up of bentonite, a clay deposit originating from volcanic ash. The shelly creatures clearly had to contend with quite a lot of environmental pressure, but the fact that limestone layers follow after each sandy or volcanic bed shows that they have been able to cope. Geologist's head shown for scale.

Images are licensed for reuse under creativecommons.org/licenses/by-sa/2.0