THE GEOLOGY OF HOLT by Professor Cynthia Burek
The Geology of Holt is dominated by two time periods the Triassic (251-199.6million years ago) and the Quaternary (2million years ago - present).
Both periods in the Holt area are dominated by sedimentary deposits. We have no igneous or metamorphic rocks in this area.
At this time Holt lay north of the Equator in the tropical zone around the latitude of the Sahara today. The sediments laid down in the Triassic were sand and muds which after the rock forming process become sandstones and mudstones. These can be clearly seen under Holt castle. They were deposited by a huge river flowing north from some high mountains in what is now Brittany. As the river flowed north, the deposits became smaller in size so we lack the large pebbles which can be seen for example in the Stoke or Stafford area. The rocks are red as the individual colourless quartz sand grains were coated in an iron oxide called hematite (Fe2O3). Some are well glued together; others are not; hence the difference in resistance to weathering by rain and wind.
We have no evidence for what happened in Holt between Triassic times (roughly 200 million years ago) and the Quaternary (2 million years ago) and this non deposition of material is referred to as an Unconformity.