The Rocks of Sark, Herm, and Jethou

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Abstract
1. Introduction .—Sark, more fortunate than Guernsey, has the advantage of a good sketch map, which was published by Professor Liveing in vol. iv. of the ‘Proceedings of the Cambridge Philosophical Society.’ The account of the geology which accompanies that map notices the principal feature, one singular and possibly unique, namely a series of conspicuously banded hornblendic schists between an upper and an under gneissose series; that is to say, there seems to be a series which is presumably stratified in the midst of apparent gneiss. Thinking that such a succession might throw light on some problems of “metamorphism,” I undertook a careful examination of the island; and the widespread interest now taken in ‘Archæan’ rocks emboldens me to give a brief account of my results. I owe a debt of gratitude to Professor Bonney for frequent and invaluable help. The appended map (fig. 1) shows a diamond-shaped area about two miles long by one and a half broad, united at its southern end by a narrow isthmus to another about one mile long. This neck, called the Coupée, 200 feet above high-water mark and about 8 feet wide at the summit, is one of the island sights. The weather is rapidly cutting it down, and but for the roadway built up along its knifeedge the two areas would by this time be practically separate. Even between two of my visits a landslip had seriously increased the degradation. Previous writers have pointed out that the same action in a less advanced

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