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EEV. E. HILL ON THE EOCKS OP 



24. The Bocks of Saek, Heeh, and Jethou. By the Bev. E. Hill, 

 M.A., F.G.S., Fellow and Tutor of St. John's College, Cam- 

 bridge. (Bead March 23, 1887.) 



Contents. 



1. Introduction. 



2. The Hornblende-schists. 



3. The Creux-Harbour Gneiss. 



4. The overlying Granitic Rock. 



5. "Veins and Dykes. 



6. Herm and Jethou. 



7. General Conclusions. 



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 Philoso- 

 phical 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 ' Archaean ' rocks emboldens me to give a brief account of 

 my results. I owe a debt of gratitude to Professor Bonney for fre- 

 quent 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 Coupee, 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 knife- 

 edge 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 stage is proceeding at the northern ex- 

 tremity (by the cleft leading to the Boutiques Caves) ; while on the 

 west the separation of Brecqhou is complete, and on the east rocks 

 called the Burons are relics of the final stage. But, in truth, the 

 like has been happening all round on every side ; islets, rocks, and 

 shoals in almost every direction are witnesses of the progress of 

 destruction. The rock, though hard, is traversed by numerous 

 fissures (usually faults of small throw), and to these are principally 

 due, as well this destruction as also the abounding pillars, arches, 

 and caverns which give to the scenery of Sark such singular 

 charms. Guernsey boasts but a single cave of importance, while 

 Sark has several of the first order, and not a bay there is without 

 two or three of at least some interest and beauty. 



