of Guernsey. 



37 



digiously active in Guernsey. It has been shattered or torn by 

 earthquakes or upheavals, and the rents filled either at once with 

 molten lava, or slowly by deposits from steam or water. 

 Hence has arisen the network of dykes and veins which seam 

 the sea shores and cliffs, some are of very great size, one at 

 the Gouffre landing is 30ft wide, and there are still larger 

 masses at Bon Repos and Pleinmont. They are principally 

 basalt, diabase, or diorite ; Granite and elvans are frequent ; a 

 pink felstone occurs at Castle Cornet, and south of that ; mica 

 trap, rare in Britain is found in brown rocks on the shore at 

 Moulin Huet. Castle Cornet, L'Eree, and the north point of the 

 island, are localities which offer much variety in a small space. 



A student of Palaeontology will find nothing to collect, he 

 must content himself with the recent shells of the " shell- 

 beach " on Herm. The rocks of Guernsey all belong to that 

 most ancient of formations, the Archaean ; no later sediments 

 exist save the latest, those now forming peat-sand and gravel. 



In Sark all the phenomena above described may be wit- 

 nessed in even higher perfection. In addition there are the 

 Creux Derrible and the Pot, shafts on the hillside opening at 

 their bases on to the shore ; these originate from sea-caves 

 whose roofs have fallen in. The cliffs of Sark are mainly Horn- 

 blende schist; there is some Gneiss at the Pier, and granite 

 on Little Sark ; and at the north end. A dyke of mica-trap 

 occurs at Port du Moulin. 



In the northern division of the Island of Guernsey, Granite 

 occurs near Grand Havre at Mont Cuet, and l'Ancresse. 

 Syenitic Granite in the Vale Quarries, and through the centre 

 of St. Peter-Port. Elvan veins intrude with the Granite, Red 

 Granite is found from Cobo to Grandes Rocques. On the East 

 from Long Store to Yale Castle are various Hornblendic Rocks, 

 (locally named Bird's Eye). The southern part, from a line 

 drawn from Castle Cornet to Vazon Bay, consists of various 

 Gneissic Rocks traversed by intrusive veins of Trap, Porphyry 



