The Prendergast gravel sheet

The site of the new high school in Haverfordwest, now completed.  In 2020/21 I tried to get permission to examine the exposures while things were still visible -- but it was at the height of the pandemic, and the pass never came through.  An opportunity missed........

Last year I speculated on the nature and extent of the vast sheet of sands and gravels in the Haverfordwest area:

https://brian-mountainman.blogspot.com/2021/06/outwash-gravel-sheets-in-central.html

When I went for my vaccination in the building next to the site there was a spoil heap just over the fence, made up of sands and gravels and many large boulders up to 1m in diameter.  Although I never got to see the excavations, this convinced me that the gravel sheet across this landscape is made up not just of fine-grained bedded sands and gravels but also debris associated with in situ ice wastage.  In other words, the glacial source was quite local, and not distant.  That's an important point when we are trying to understand what went on here during the Devensian.

Right on the left hand edge of the above photo, where we see a road with a sharp bend, was one of the playgrounds we had as kids -- a steep gravelly slope which was great to slide down but a bit precarious to climb up.  This was not far from the trenches used for WWI training purposes and the hut used by the cadets.  Grid ref SM 956158.  This was actually an exposure of the fluvioglacial gravels -- the edge of a gravel terrace looking down on the Western Cleddau river.  The gravels were still exposed in the 1950s and 1960s, and when I last had a chance to examine them -- in 1963 -- there were about 3m of deposits visible: 

3.  Colluvium, soil and slopewash, dark brown with high organic content and more silt and clay.  C 45 cm thick.  

2.  A gravelly layer c 50 cm thick of rounded and sub-rounded cobbles and boulders

1.  A  lower gravelly horizon c 2m thick with rough bedding (mostly gravel of mudstone fragments) including several patches of larger blocks of sub-rounded rocks up to 25 cm in diameter. 

Broken shale bedrock at base.

None of the deposits was cemented, there were no shell fragments, and there was a good proportion of far-travelled igneous rocks that must have come from the Trefgarn Gorge area and also flint nodules.  I identified almost 30 different rock types in my stone collection exercise, and concluded that the deposit was possibly a fluvioglacial deposit laid down subglacially, with a possible flowtill resting on the lower gravels.