374 Geological Survey of the Island of Jersey, 



by having ascended the summit of the coast-range, affords no 

 means of ascertaining the precise junction. This slate, as 

 well as the limestone, dips north and west ; it corresponds, in 

 every respect, to the Plymouth transition slate in external 

 structure, and internal composition : at Granville it becomes 

 decided grauwacke, sometimes as 73, and the conglomerate * 

 72, when immediately at the peninsular on which the town 

 stands, and at other times 70 and 71. At 73, it is intersected 

 in every possible way by minute and very abundant quartz 

 veins. These last, and the numerous pebbles of the same, oc- 

 curring in the conglomerate, together with the very siliceous 

 character of 73, prepares the way for what, perhaps, was the 

 origin whence the veins were deposited, and the pebbles torn, 

 i. e. quartz rock j, 75, 76. This is found one mile south-east 

 of Granville, on the south side of the valley, under the road to 

 Avranches, in cliffs of such dimensions as to warrant the pos- 

 sibility of its having some extent, especially when the large 

 deposits of the same, en debris, covering the flat hill-tops near 

 Granville, are taken into consideration. It dips north and 

 west, underlying the grauwacke slate, which completely inter- 

 cepts it seaward, sometimes in the shape of 74, at other times 

 as usual. 



About half way between Granville and Avranches, the 

 slate ceases, as it overlays the rock 77, 79. Avranches itself 

 stands on a high abrupt hill, composed of this last and 78 (of 

 which I am quite uncertain as to the extent). Following the road 

 to Mount St. Michel, at the ferry, you again find slate (80), 

 dipping south-east J, lying east and west, covered with a debris 

 of mica slate, &c. 79 a. The mount itself is composed of 79 

 and 81 , and as this last contains quartz, felspar, hornblende, 

 and mica, there can be no objection to terming it granite. 

 On the authority of my guide, from its external appearance, 

 and correspondence of situation, I have good reason to think 



* I cannot leave this without pointing out how completely this con- 

 glomerate, in the siliceous extreme of the clay state, seems analogous to 

 the Jersey breccia, as accompanying the argillaceous variety. 



t This rock is, probably, at no great distance from the west of Jersey, 

 (compare 22 a, and 22 b, with 70, 71, 73) as the beach at St. Ouen's Eay 

 is, in a great measure, covered with its pebbles. 

 • t Apparently overlying the Avranches rock. 



