THE ROCKS OF ALDERNEY. 237 



stone and the sandstone is slight ; the sandstone is altered at 

 the contact and beeomes a species of white quartzite. At the 

 extremity of the island I saw another dyke of the same nature 

 running out to sea, which may be a continuation of those in 

 Maunez Quarries. 



Returning along the south-east coast of the island I came 

 to the quarry under Essex Castle, where, as well as on the 

 adjoining beach of Longy Bay, I noticed occasional seams of 

 pebbles in the sandstone, these pebbles being mostly small, 

 but occasionally reaching three or four inches in their longer 

 diameter. They consist of quartz, diorite, and felsite. 



After having visited the town I found I had yet a short 

 time at my disposal ; I walked along the coast to the west of 

 the breakwater, and noticed the intrusion of the felsite or 

 quartz-felsite veins in the diorite. These veins, further west, 

 become so thick and numerous as to seem to form the princi- 

 pal rock in that part of the island, being the " porphyry " 

 referred to by MacCulloch and Ansted. 



I noticed raised beaches all along the eastern extremity 

 of the island, also in Longy Bay, where it is overlaid by 

 " head." These beaches correspond in appearance and position 

 with the " low level " beaches in Guernsey. A very extensive 

 raised beach, overlaid by " head," occurs in Plate Saline Bay 

 (somewhat resembling that near Fort Le Marchant in this 

 island). The pebbles are chiefly local rocks, some being 

 about a foot in diameter. A large proportion of the pebbles 

 do not lie horizontally, but dip inland at an angle of about 

 60°. Flints are found in this and other raised beaches. The 

 present beach of Plate Saline Bay contains a considerable 

 proportion of flints, mostly small. 



The age of the Alderney sandstone or grit has been 

 discussed in Rev. Hill's paper, read before the Geological 

 Society, and I referred to it in the paper which I read before 

 you about eighteen months ago ; but I have thought that by 

 means of a diagram the subject might, perhaps, be made some- 

 what clearer. I have, therefore, shown on the annexed diagram 

 the correlation of the rocks of France with the typical series 

 of England and Wales, according to M. Bigot, and also with 

 the Channel Islands rocks. By the investigations of M. Bigot 

 and Rev. Hill the following points appear satisfactorily es- 

 tablished : — 



1st. — That the Alderney grit is identical with the " Gres 



feldspathique" of the northern part of Contentin. 



2nd. — That the "Gres feldspathique" immediately 



underlies the "Gres armoricain," the oldest 



