A Geological Field Trip – June 2002

by Roslyn Malcolm - aged 13yrs and daughter of NW member, Andy Malcolm

The following are photographs and brief descriptions of some geological features to be found in a limestone quarry (Trowbarrow Quarry near Silverdale) and on the rocky foreshore below the cliffs at Heysham Head. These limestone and sandstones formations were all formed during the period known as the Carboniferous, around 340 million years ago.

Trowbarrow Quarry

This photograph is of a colonial coral and a “stick” trace fossil formed by burrowing animals (like worms). The colonial coral fossils have been preserved in the position in which they grew millions of years ago. The presence of the coral gives a clue to what the environment was like at the time they lived, ie clear, warm, tropical, shallow seas.

This photograph is of a large bedding plane, known by climbers as the Main Wall. It is covered by a lot of “stick” trace fossils (seen in the previous photo). Further up the cliff, but not visible in the photograph there are several fossil shells.

This photograph was taken looking down the quarry towards the north. It clearly shows the different layers of limestone in a vertical plane. Sedimentary layers such as these are deposited in a horizontal plane but what has happened here is that the layers have been subjected to pressure and tension during earth movements causing them to be folded into what is known as a monocline. The younger beds are to the right, or east, of the picture.

Heysham Head

This shows sandstone layers and their bedding planes dipping at a low angle which we were able to measure using a compass clinometer. On the uppermost layer to the right of the picture, there are some scratch marks caused by glacial movements, which are called striations.

This photograph was taken at the foot of the cliffs. It clearly shows the interbedded layers of sandstones and mudstones or shales. The mudstone is in the thinner layers which are very fine and crumbly, to the extent that it is easily broken by hand. The difference between mudstone and sandstone is that the grains making up the mudstone are very small in comparison to those in the sandstone, which gives us a clue as to what the environment must have been like at the time of the mudstone deposition ie still water.

Another picture showing the different sedimentary layers of sandstone and mudstone. (Roslyn crumbling some shale)

The final photograph is of a trace fossil. It is known as a Diplocraterian and has been formed by the upward and downward movement of an animal in the sand.