1877.] of the rochs of the Channel Islands. 77 



quarry belonging to Mr Mowlem, on the west side of Delancy Hill 

 near St Sampson's. It is about 5 feet thick where it is exposed, 

 evidently stratified, and dipping towards the north-west. It thins 

 out on the east side, but appears to increase in thickness to the 

 west. The quarry has been wrought down to it through some 

 80 feet of grey syenite, and the quarry men told me they had 

 tested the thickness of it, and finding that it increased in thick- 

 ness to the west they did not attempt to remove it. They are now 

 working on the south-east side and underneath it, merely removing 

 it as it falls. 



The chief mineralogical diffprence between the upper and the 

 lower division of the rocks is that the upper contains a good deal 

 of quartz and some mica, while the lower contains scarcely any 

 quartz and no mica, but a great deal of hornblende. 



In the neighbouring island of Sark, only about 7 miles distant \ 

 the lower hornblendic beds have not undergone nearly so complete 

 a crystallization. The greater part of Sark consists of a hornblende 

 schist, overlaid at the north-west by a gneiss not unlike that of 

 Guernsey, but less red in colour. I have no doubt that these are 

 really the same beds in both islands. In the south of Sark there 

 is a grey syenite closely resembling some of the Guernsey syenite. 



There are plenty of volcanic dykes which produce some of the 

 characteristic features of the coast scenery, but they mostly cut 

 clean through the metamorphic rocks and seem to have had little 

 or no effect upon the parts in contact with them. The greater 

 part of these dykes are of a fine grained compact greenstone, not 

 more than a few feet thick, and they are disintegrated by the sea 

 and weather much more rapidly than the metamorphic rocks. The 

 promontory on which Richmont barracks stand between Perelle 

 and Vazon Bays is cut through by some of these greenstone dykes. 

 The gneiss there is highly hornblendic. On the Vazon Bay side it 

 retains its stratified character, while on the Perelle Bay side it 

 forms a highly crystalline syenite shewing no trace of stratification. 

 It may be questioned whether the dykes have anything to do with 

 these characters. I think not, because they extend to much too 

 great a distance from the dykes, and because in other places no 

 such effects are produced by the dykes. 



There is another set of dykes of a different material, consisting 

 of a very compact reddish felspathic matrix with small lumps of 

 quartz imbedded in it. These dykes are seen at the bathing-place 

 by St Peter Port, where the road is cut through them, and they 

 run on through the island on which Castle Cornet stands. These 

 red dykes are not parallel to the greenstones ones, and must have 



1 The actual distance on the shortest line as measured on the Admiralty Chart 

 is a little less than 6f miles. 



