MGA field trip to Quarry Bank House Secret Garden - Styal Mill - June 2008

Some 30 members, guests and Rockwatchers came along for a great field day, led by Fred Broadhurst in the morning and Fred Owen in the afternoon on Saturday June 14th.

At the invitation of the National Trust, the two Freds have been working on the geology of the newly opened quarry garden for a couple of years. They have written a leaflet about the geology, a laminated précis of which is now being lent to visitors to the garden by the NT.

We spent the morning in the quarry garden. There are several superb exposures of Triassic sandstones in the “Secret Garden”. We had the benefit of both the leaflet and their expertise in explaining the depositional environments. These well-bedded sandstones were formed in the middle of a huge continent, situated at 20ºN. Some are water-lain following sporadic downpours and flash floods, others are wind blown aeolian dunes. The bright red colour is due to a coating of ferric oxide on the sand grains, which also provides the cement to “glue” the rock together.

Subsequent earth movements uplifted and tilted the strata, leaving them with a dip of 49°, far greater than the original angle of repose of 25º to 30º for sand grains on a wind-blown dune.

Triassic sandstones in the Secret Garden

After lunch Fred Owen led us round the Styal Park Geological Trail that he devised as part of his studies in 2000.

Nature has had its way with some of the exposures, for the River Bollin is very active here and has removed some of the riverbank paths, so that you can no longer get up close and personal with some of the rocks. However Fred O’s intimate knowledge of the terrain enabled him to show us subtle geomorphological features that the casual visitor would have missed. We had a good look at deposition currently (no pun intended) taking place in the river and were able to relate that to structures found in the rocks. We did get close to a big exposure in Worms Hill Quarry and here Fred B demonstrated how the old quarrymen extracted the big blocks by hacking out a trench all round them, chisel marks show the direction of their blows!

You should all have received a copy of Fred Owen’s Geo trail in the past, if not Fred O still has some to dispose of.

We hope to hold a MGA “event” at Styal next summer ... watch this space!

Mary Howie