Watchet is very fortunate in its geology, lying on local lias rocks, set down 200-215 million years ago, for within these rocks are a variety of fossils. The lower liassic sedimentary beds were formed in the first part of the Jurassic, merging with the end of the earlier Upper Triassic period.
The Museum is able to display a wide selection of locally-found fossils, many picked up by people walking on the foreshore. Ammonites and Gryphaea are abundant, and fossilised coral, fish, oysters and plants are also represented amongst the collection.
The author Daniel Defoe visited Watchet in 1724 and was puzzled by the fossils he found on the beaches and wrote:
"Walking on the shore at Watchet I discovered among the large gravel great numbers of stone, fluted in imitation of shells of fishes of all kinds. Some I have seen as broad as a pewter dish, and again others no bigger than a pepper corn . . . they lie there in great plenty."
A star attraction within the display is a near complete lchthyosaur, a marine creature that swum in the warm seas that were Somerset millions of years ago. Recent finds include a Plesiosaur rib bone discovered in 2008 along the shoreline near Warren Bay, and vertebrae and coprolites from the same species.
It must be stated that although it is permissible for anyone to collect fossils along the shore, it is forbidden to hammer the cliffs or rocks to obtain samples.
An insight by local geologist Dr. Eric Robinson
In the geological world, Watchet is well known a place where the red rocks of the Trias pass upwards into the grey marine rocks of the Jurassic (the Lias). The rock sequences are easy of access and can be collected.
Appropriately, Market House Museum has on display in its limited space all the typical fossils which can be found on the shores. Two display cases will introduce you to ammonites, "Devil's Toenails" (the popular name for Gryphaea, a fossil oyster), several kinds of bivalves, and fragments of bone of sea reptiles such as Plesiosaurus or Ichthyosaurus, before you set out collecting for yourself.
With our huge tides on the Bristol Channel and the softness of the local rocks, our cliffs are regularly refreshed by erosion. Safety demands that we don’t hammer or collect from the eroding cliffs. Nature provides specimens from the beach screes and the beach material sorted by the tides. New finds are always possible from the shores as fresh rocks are uncovered and the museum will help with identifications. To provide encouragement, new discoveries are on show in the cases. Other than fossils, our coast is famous for mineral gypsum, usually referred to as alabaster. Seams and large blocks occur in the red marl cliffs of West Beach and Warren Bay (Longsands). Again, as our cliffs are crumbling, especially after wet weather, collect your specimens from the fallen debris where it will have been shaped and isolated by the tides. Locally, alabaster has been carved by Watchet craftsmen. Some of their work is included in our displays.
Explanatory A4 sheets are available at the Museum explaining in everyday words and diagrams the geology of Watchet. Helwell Bay, the streets and walls of the town, and finally, the Heritage Lottery funded Mineral Line served the iron mines of the Brendon Hills (NW Exmoor). There is also a folder explaining the Watchet Jubilee Geological Wall on the platform of the station. Typical fossils and rock types of our area were built into the base of the old signal box, a unique way of advertising our rocks to the 40,000 travellers who come by train every year to Watchet.