MEETINGS. 331 



taming felspar crystals, giving it a porphyritic aspect. These 

 crystals may be derived from a fused portion of enclosing rock, 

 having become mixed with the inclusion. The enclosing rock, 

 though evidently an igneous rock, is slightly gneissic, and occa- 

 sionally reminds one of the gneiss of the southern coast of 

 Guernsey. In this granite or syenite there are also numerous 

 veins of a more gneissic and schistose character, and occasion- 

 ally almost slaty. These do not, however, seem to be true veins, 

 but are probably similar in origin to the slaty rocks noticed at 

 Bocquaine and Sommeilleuse, being due to pressure and crush- 

 ing of the rock in early ages and subsequent reconsolidation. 

 Bocks of this nature have been termed " Mylonite," from the 

 Greek word for a mill. 



A vein of felsite 2 feet wide crosses Crevichon. Some 

 smaller veins Avere observed ; one of these in the first cove to 

 the west of the landing was of a soft nature, and presented a 

 banded appearance. 



No veins of diorite (so abundant in Guernsey) have been 

 noticed. 



MICA TRAP VEINS. 



Two of these occur close together some distance to the 

 north of Bec-du-Nez. One is 10 feet in width, with mica in 

 rather large flakes. Its erosion has given rise to a small but 

 picturesque cave. Its direction is N.E. to S.W. The other 

 vein, a few yards to the N., is much smaller but of similar 

 character, and is probably a branch of the larger one. A 

 very wide vein of mica trap is found in Monument Bay, south 

 of the marble caves above described, running E.N.E. to 

 W.S.W., close to and parallel to the well-known quartz vein 

 which crosses the isthmus near Doyle's Column. The mica 

 flakes are small and not very noticeable, but the rock exhibits 

 the characteristic roughness and fantastic weathering. 



Jethou. 



Mica trap dykes abound. The following were noticed on 

 the west coast, going from north to south : — - 



(a) Direction, N.E. and S.W. Width, 4 feet. 



(b) Direction, N.W. and S.E. Width, 10 feet. 



The rock on each side is altered to a distance of 

 10 feet, 



(c) Direction, W.N.W. and E.S.E. Narrow. 



(d) Direction, E. and W. Width, 14 feet, 



(e) Direction, N.E. and S.W. Width, 11 feet, 



(f) Direction, W.N.W. and E.S.E. Width, 4 feet. 



This dyke is remarkable on account of its un- 

 decomposed condition. 



