32 ROCKS OF THE CHANNEL ISLANDS. 



two or three dykes of a dioritic nature cut the conglomerate. 

 These, however, are quite different in appearance to the 

 Archaean diorites above referred to, and are the newest rocks 

 in Jersey. Almost the whole of Guernsey, in my opinion, 

 belongs to the Archaean system. The northern part of the 

 island consists of diorite sometimes approaching hornblende 

 rock with syenitic and granitic veins. The southern part 

 consists chiefly of gneiss, but diorite occurs in various parts. 

 Many, probably the greater number of geologists, consider 

 gneiss to be a metamorphosed sedimentary rock, but several 

 of late years are inclined to regard it rather as a rock of 

 igneous origin like granite, which has been deformed and 

 acquired a fluxion structure under enormous pressure. 

 Whatever may be the case in other districts, the appearances 

 in Guernsey seem to me to favour the latter view. The 

 diorite appears to me to be associated with the gneiss in the 

 form of inclusions rather than of intrusions, and I am inclined 

 to consider the gneiss as a modification of the syenites and 

 granites (such as the coarse granite near L'Islet) of the 

 northern part of the island. Some of the gneiss towards the 

 west of the island, as at Richmond, is highly granitoid, while 

 some of the syenite, as at Baubigny, has a gneissic structure. 

 There is a considerable patch of rather fine-grained granite 

 east of L'Ancresse clearly intrusive in the diorite, which also 

 shows a gneissic structure, apparently the result of compres- 

 sion, and veins of similar granite intrude in the gneiss, which 

 show the same structure though to a much less extent than 

 the surrounding gneiss, and not always in the same direction. 

 This granite, though of later date than the diorite and gneiss, 

 may perhaps be put down as Archaean. The rocks of Sark 

 consist chiefly of gneiss and hornblende schist, the latter 

 much resembling in composition the Guernsey " Birds Eye " 

 diorite. The gneiss appears to be intercalated in some places 

 with the schist, and resembles that of Richmond previously 

 referred to. The schist, as well as the gneiss, is in my opinion 

 a modified igneous rock. However this may be, both the 

 gneiss and schist probably belong to the Archaean system, 

 to which Rev. Hill also refers the granite of Herm and Jethou, 

 and the syenite or granite of Alderney. The Ecrehos are said 

 to be composed of gneiss, probably also Archaean. 



Next in succession to the rocks above described, I would 

 place the"Argillite," found in Jersey, also called "Argillaceous 

 Schist " and shale, and by M. Noury " Gres feldspathique." It 

 is an unquestionable sedimentary rock. The bedding is 

 generally very distinct, and it consists of alternating light 



