A Geological Commentary

We were very saddened to learn of the untimely death of Fred Broadhurst in 2008 and will miss his invaluable help
in understanding the development of settlement on the underlying Geology of the area.
The following commentary was provided by Fred Broadhurst and Morven Simpson in 2001:

" Beneath the soil, there is a layer of Boulder Clay, containing a variety of pebbles and rocks, 'Erratics' left on the site after the glaciers retreated 10,000 years ago, including granite, volcanic tuff and other rocks from the Lake District or southern scotland.

The underlying rock is sandstone, which is locally known as Woodhead Hill Rock, from the Late Carboniferous Age about 315 million years ago. It would have been deposited on a river delta.

Trench 10 is a geological feature, where a ferroan calcite cement in the sandstone has been dissolved by groundwater, leaving the "ditch" filled with sand. One of the rocks in T10 was ganister with a well preserved fossil root sytem. Coal has also been found. Below the sandstone are layers of consolidated clay, which act as a damp proof course. The base of the well is probably at this level."

Fred described the large area of open excavation in the field as one of the best examples of deposition in a river delta that he had seen.

"The sandstone rocks are over 300 million years old, but were subsequently buried under later rocks. At sone time, where we stand today would have been a mile or two below the surface of the earth. Erosion and other geological disturbance (plus the work of archaeologists in removing a foot of soil!) have now brought these rocks back to the surface where we can look at them.





Points of note in the geology are:

Bedding plane surfaces
Which mark the tops of individual sandstone (originally sand) layers.

Joints
These are approximately at right angles to the bedding planes, often remarkably straight, formed by expansion of the rocks
as a former thick rock overburden was removed by erosion.

Cross-stratification
Is where the bedding is seen, locally, to be tilted relative to the adjacent bedding planes...
formed by the deposition of the original sand under moving water on the down-current side of sandbanks, ripple structures etc..
of very large proportions, probably as part of a vast delta...progressively buried beneath an enormous thickness of later sediments,
transformed into sandstone by the addition of natural silica cement, then uplifted and exposed by erosion to produce the outcrops we see today"