A group of 11 made up the Brimham Rocks Geology Trip on Wednesday, June 29th. It was led by Stephen Lewis a very knowledgeable geological guide, author, and volunteer at this National Trust site.
Brimham Rocks is famous for its spectacularly exposed rock pinnacles that allow a three-dimensional insight into a complex ancient fluvio-braiding system. Whilst its 18 century visitors attributed the bizarre formations to the work of Druids, the 21st century geologists are still researching into the scientific formation of these features.
The Millstone Grit of Brimham Rocks were formed about 320 million years ago. Research in the last five years has now led to the theory that the sediments laid down at Brimham and subsequent formation of the millstone made from sand, grit and rounded pebbles of quartz and some feldspar was the result of a braided river system carrying sediment from the newly formed Caledonian mountains.
The layers of sediments were washed down by storms and due to the velocity of the layering there was no time for fauna or flora to settle, hence there are no fossils at Brimham, with the exception, of a salamander footprint.
As the river braiding changed the direction of the flow of the river, the layers of direction of sediment would also change direction and these are really evident in the rock formation on site.
Brimham is also famous for the unique flame structures that are so rare to see in Britain as illustrated below on the bottom strata.
The weight of an overlying bed forces an underlying layer to push up through its overlying bed. The resulting pattern resembles flames in a rock cross section and is the direct evidence of earthquake movement.
Around 18,000 years ago, the northern Pennines were covered by an ice cap and the stone sculptures at Brimham are a direct result of this. Rocks that stood above the ice sheet were exposed to strong glacial winds blowing off the ice caps. These winds carried fine sand particles that effectively sandblasted the exposed rocks, creating the features that are so characteristic of this National Trust site.
The sunshine and dry weather added to the pleasure of the day. It was a fabulous and informative tour and well worth a visit.
Report Stella Hughes
Photos Ian Hughes