22 MEETINGS. 



ROCKS. 



1. — Granite Veins in Talvane near Ruettes Villa, Castel. 

 Talvane veins abound in nearly all parts of the island, 

 cutting both the gneiss of the southern parishes and the 

 syenite and diorite of the northern, but they have not been 

 observed in the Cobo granite. On the contrary, these veins 

 when occurring in the gneiss adjoining the granite are cut off 

 by the latter, as may be seen in Mr. Falla's gravel quarry 

 referred to at page 329, volume 2. An example of granite 

 veins in talvane occurs in a quarry at the back of Mr. H. 

 Duchemin's property, Ruettes Villa. Although in this case 

 the connection of these granite veins with the Cobo mass 

 cannot be traced, it probably exists. The talvane diorite 

 occurs as a vein 50 feet in width intrusive in gneiss. Its 

 strike is S. 20° W., its dip nearly vertical, but varying. This 

 talvane is intersected by numerous jointing planes, the most 

 marked of which have a strike of E. 65° S. with a dip of 70°, 

 but two of the jointing planes belonging to another set nearly 

 at right angles to the first mentioned have served as channels 

 for the intrusion of thin sheets of granite, one an inch and a 

 half thick, the other three-quarters of an inch. These veins 

 are very even, but the thinner one is displaced by faulting to 

 the extent of about a foot. The fault is caused by the slip- 

 ping of the rock along a number of the planes belonging to 

 the first mentioned set closely adjoining each other. Thus 

 the series of events appears to be as follows : — 



1. The intrusion of the diorite in the gneiss. 



2. The formation of the second set of jointing planes, 



either accompanied or succeded by 



3. The intrusion of the granite in the diorite. 



4. The formation of the first mentioned set of jointing 



planes, either accompanied or succeeded by 



5. The faulting. 



2. — Lihou Island. 

 The predominating rock is porphyritic gneiss. This 

 gneiss is also found on the opposite mainland and is exposed 

 at every point of the causeway uniting Lihou and the main- 

 land. Thus a good opportunity is afforded of noting the 

 gradual change in the foliation. On the mainland the rock 

 is but slightly laminated, but going westward the crystals of 

 felspar become more and more flattened into lenticular patches 

 and eventually into thinner and thinner lamina?. These 

 laminae, at the extreme west point of the island, have a dip of 

 65° S.E. 



