88 MEETINGS. 



5. — Cave at Les Thielles. 



A cave west of the arched promontory has been visited. 

 It is due to the erosion of a black diorite vein in gneiss. Its 

 direction is east and west. The opening is almost blocked up 

 by falls of rubble forming a cove about ten feet high, some- 

 what similar to that at the entrance of Creux Mahie. The 

 opening above the cove is only sufficient to permit of a person 

 crawling through, but once within there is plenty of space, 

 the cave being 63 feet long, 20 feet wide at the entrance close 

 to the base of the cove, narrowing to 4 feet. The height was 

 not measured, but is considerable. One side is perpendicular, 

 the other slopes at a high angle, resembling in this respect 

 also the more considerable cavern at Creux Mahie. 



Erosion on the West Coast of this Island. 



Mr. J. J. Carey has communicated a note" on the erosion 

 of the coast on the west of the island, which has been consi- 

 derable of late. The cliff at Rocquaine, of which a section is 

 given in this report, has been further cut back during the 

 October storms, and near Lihou Island fresh exposures of 

 raised beach have been made. In this locality a small cave 

 8 or 9 feet deep has ceased to exist, owing to the removal of 

 its sides by the action of the sea. The Geological Section 

 are thankful to Mr. Carey for having placed marks in certain 

 portions of the coast most exposed to erosive action, by which 

 it is hoped the extent of land which may be henceforth 

 removed will be ascertained. 



C. G. De La Mare, Sec. Geo. Sect. 



Mr. A. Collenette having transmitted some specimens of 

 Guernsey rocks to Mr. W. W. Watts, Geological Survey of 

 Great Britain, Jermyn Street, London, has kindly permitted 

 the publication in these Transactions of the following report : 



Sent July, 1895. 



1. E. 2,554.— "Vein Diorite, Jethou."* A sericite 

 schist with a few eyes of quartz. No original structure left. 



2. E. 2,555. — " Porphyritic Quartz Syenite, Richmond." 

 This is a rock showing porphyritic crystals sometimes a 

 quarter of an inch across of plagioclase felspar and made up, 

 as the microscope shows, of abundance of smaller crystals of 

 the same mineral, a few large and many small crystals of 

 augite all set in a minute matrix. There is much iron ore in 

 the slide. We are now calling rocks of this character Por- 



* This rock is referred to in the report for 1894, page 331, lines 6 to 13. 



