Lithological Analysis

Cedar Road Quarry in 2014

In my last post, I briefly described my surprise at seeing the overgrown condition of this site and my first job at Cedar Road Quarry was to try and find a place where the students could make drawings and take measurements of the rocks – but this wasn’t so easy. Whereas before, there was an expanse of red rock, there were now insurmountable brambles, as well as nettles, and no obvious access to any rock face.

We soon decided that the students’ time, at this site, would be best spent examining the rocks at close hand and, once I had demonstrated that the brambles and nettles could be trampled and a path cleared, albeit with a small scratch or two, the students threw themselves into the task. 

Sandstone and mudstone

Although a geological hammer was at hand, taken from the toolbox by a boy who wanted to use it, I showed them that a small sample of this sandstone could be broken off by hand and easily crumbled with the tips of the fingers. 

They learned how to distinguish the sandstone from the thin discontinuous layers of mudstone that occur within it and to note the differing weathering characteristics of these rocks, as well as seeing the variety of large and small sedimentary structures that can be found within them.

Each took a small piece of sandstone and mudstone to a grassy area, where they used their hand lens to examine and analyse them and make notes in their science books. Although each had laminated grain size charts, I showed them my “old fashioned” Wentworth Grain Size Chart, which has actual grains of silt and sand glued to stiff cardboard. With their eyes closed, the students were encouraged to rub the card and to appreciate the value of using more than vision to investigate the physical properties of rocks.

Grain size charts

Also, to their great surprise - and to the initial disgust of some - I then proceeded to lick the small fresh piece of sandstone that I had taken from the rock face. I had first learned this when making a map of the Borrowdale Volcanics, to highlight the texture and minerals contained in the rock, but have subsequently discovered that the taste of a fresh piece of rock can vary considerably, as well as the smell that is generated when a stone is cut with a diamond saw or ground with abrasives.

Having emphasised that it is only safe to do this with fresh rock, and that this should only be done once you have gained sufficient knowledge of geology and mineralogy, I was later surprised to discover that one of the boys actually tried this.

An introduction to the science of geology