Geology

Abstract

Historically, the British Channel Islands lay outside the scope of the national geological surveys of both Great Britain and France but were studied by a succession of geologists, British, French, and local, from at least 1811 onwards. These established that the islands reveal a terrain different from other regions of the British Isles and form part of the Armorican Massif, of Precambrian to Paleozoic age, that forms much of Lower Normandy and Brittany in nearby France. This region comprises metamorphic and igneous rocks together with a range of Paleozoic strata, the bedrock having a thin and patchy superficial cover of Quaternary sediments. Rocks of Mesozoic and Tertiary age are largely absent. When they seized the islands in 1940, German forces had access locally and via university libraries in Germany and France to a wide range of published information that revealed a developing understanding of the kinds of rocks to be found on the islands, and the times and processes involved in their formation. The distribution of the major rock types had been mapped at different scales and detail in the different islands, but provided a basis of ‘pure’ geology that could be enhanced and adapted to meet German military engineering requirements.