The narrow strip of country forming the southernmost peninsula of South Devon, and extending from Start Point westwards to Bolt Tail, has been the subject of repeated enquiry by various geologists since the first report on the geology of Devon by Sedgwick & Murchison. On the north this area is bounded by rocks the Devonian age of which is attested by definite organic remains. Whether the rocks of the Start peninsula themselves are also of this age, or whether an older group, has been much discussed, and no small part of the literature is devoted to this subject, apart from any exhaustive study of the rocks themselves. Prof. T. G-. Bonney1 appears to have been the first to apply microscopic petrographic methods to the elucidation of the rocks themselves, and, following him, Miss C. A. Raisin 2 has also contributed researches on the same lines. But no adequate account of the mineralogical nature of the peculiar Green Schists of the area was forthcoming until Sir Jethro Teall and Dr. A. Harker l examined sections of the rocks collected by other observers. In any interpretation of the structure of this tract of country, the early observers were at a disadvantage, in the fact that no adequate geological survey of the district had been made. The task of mapping the area was undertaken by the Geological Survey, the results appearing in the 1-inch map by W. A. E. Ussher, published in 1898. Since that date the area has been mapped on the