The Geology of Southern Guernsey

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Abstract
Guernsey, the second largest of the Channel Islands, has been described geologically in varying amount of detail by a number of previous investigators, who for the most part confined their attention to the northern portion of the island, and there are only scanty references to the metamorphic complex forming the southern portion. In 1884 the Rev. Edwin Hill & Prof. T. G. Bonney (6) announced the result of their first visit to the island, and gave a few general notes relating to the southern gneisses which they believed to be, as a whole, comparable with the Laurentian Gneisses of Canada. No attempt was made to distinguish between the various types of gneiss which are now known to occur in that area. In a paper on Alderney Canon Hill (7) discussed the age of the Channel Island rocks and, incidentally, announced his conclusion that the ‘Guernsey Gneiss’ is mostly—perhaps all—of igneous origin, but subsequently crushed. The conclusions of the two writers above mentioned may be summarily stated as follows:—In all the islands there are plutonic rocks—diorites and hornblende-granites—which are posterior to the gneisses and other dynamically altered rocks, but are believed to be pre-Cambrian, since in Jersey these rocks are overlain by the Rozel Conglomerate (basal Cambrian) and in Alderney are succeeded unconformably by grits correlated with the Conglomerat pourpré (Ordovician). The main object of the present paper is to give a description of the distribution, field relations, and petrographic characters of the different types which together make up the metamorphic

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