1922.] GEOLOGY OF ALDERNEY. 131 



Lihou Island. It stretches along half-a-mile of a wild part 

 of the coast, 250 feet in height. The breadth of this from 

 the sea inland, is not more than 200 yards at the centre. The 

 complete development of the lowest beds is seen here, but the 

 middle beds seem less developed than in the north. This 

 area is best for detailed study of the lower beds, which lie 

 on an old sea floor of granite porphyry, found at both 

 extremities of the area.. The dip is to E.S.E. at 30^. The 

 eastern border of the grits is marked by a stream known as 

 Maux. The junction shows the porphyry weathered in 

 curious angular and nodular fragments, ranging in size to 

 a diameter of eight inches. A thickness of eight feet of 

 porphyry is in this way decomposed, but not in any sense 

 sedimentary. The lowest bed of the grits much resembles 

 the Rozel Conglomerate of Jersey. Fragments, some 

 rounded, some angular, reach a size of nine inches diameter. 

 Quartz, aplite, and quartzite abound. The matrix appears 

 to be formed by siliceous binding in finer fragments of the 

 same material. 



This pebble bed continues for five feet and above it is a 

 fine micaceous purple sandstone, the finest in the Island. 



Alternations of fine pebbles, grits and sands occur, and 

 higher are the alternating bands of pink and green arkose. 

 As in Berry's Quarry, the green bands reach a thickness of 

 from six to ten inches. Berry's Quarry also has the same 

 dip to E.S.E. In the Coque Lihou area a small disused 

 quarry in the hillside contains pink grits. There is a pro- 

 bable vertical succession of 250 feet, but much of this is 

 obscured under the soil of the gorse and heather-covered 

 slopes. 



The alternating shallow water deposits in this series indi- 

 cate an oscillating, but submerging area, receiving by wave 

 action the detritus of a desert land mass. 



The Igneous Series. 



Alderney markedly instances the phenomenon noted in 

 Jersey and Guernsey by Mr. Tohn Parkinson, named by him 

 the differentiation series. The variations in the pre-sedi- 

 mentary rocks include fine dolerites, coarse hornblende- 

 gabbros, diorites, quartz-diorites, horneblende-granites, bio- 

 tite-granites, aplites and quartz. There is in addition a 

 granite-porpyhry, perhaps distinct in time, but also of pre- 

 Cambrian ag*e. It is not possible to allocate definite types 

 to such indefinite areas occupied by representatives of in- 

 creasing acidity as occur in Alderney; but the following 

 generalisation may be made provided it is remembered that 

 no area in Alderney is free from differentiation. 



