328 



REV. E. HILL ON THE ROCKS OF 



rock are often lenticular or lie irregularly upon it. The height 

 of the junction above the sea varies greatly, but this plainly is for 

 the most part due to faults. On the whole almost all the appear- 

 ances point to an unconformable overlie, none are inconsistent with 



Fig. 4. — Hornblende-schists overlying Gneiss, Creux Harbour, Sark. 



it, and I am convinced that this is the true account. The only 

 appearance in favour of conformity is the rough general agreement 

 in the dips of the two series. But I would suggest that the bedded 

 structure in the gneiss may not be original, but one which has 

 been developed by pressure, the pressure being in this case probably 

 the weight of a superincumbent mass. 



4. The Overlying Granitic Rock. — It has been mentioned that at 

 both extremities of Sark the hornblende-schist series disappears 

 below other rocks ; the same also takes place in the island of 

 Brecqhou on the west. These superior rocks are coarsely crystalline, 

 containing hornblende and white felspar in grains 0*1 or 0*2 inch 

 long, quartz often but not always, and black mica occasionally, 

 especially, I think, where decomposition is in progress. The felspar 

 shows plagioclase striping, sometimes even to the unaided eye. 

 Much of the quartz is clearly secondary, occurring along strings and 

 cracks, but much is in ordinarily distributed grains. The texture 

 i§ very highly crystalline, as much so as that of any ordinary syenite 

 or diorite. The structure and jointing are massive and irregular; 

 there is no general appearance of bedding, nor any uniformity of divi- 

 sional planes. Especially at the south end of Little Sark dark nodes 

 occut, sometimes lenticular or oval, sometimes almost spherical, which 

 consist of hornblende with some felspar in grains much smaller than 

 those of the main mass. These appearances are all characteristics of 

 an igneous origin. Nevertheless these rocks have been described as 

 metamorphic gneiss, and, as will be seen, not without a good deal of 

 justification, for the rock generally possesses a rude cleavage or ten- 



