1881.] Prof. Liveing, On the rocks of the Channel Islands. 125 



as the sea can reach is completely removed while the upper part is 

 untouched, so that the result is a long gallery with vertical sides 

 and perfectly horizontal roof. The dykes are however not all 

 of greenstone or so easily disintegrated. One of an exceedingly 

 beautiful porphyry with crystals of white felspar disseminated 

 through it, cuts into the northern promontory a little south of the 

 Boutiques. It resists weather equally well with the syenite, and 

 pebbles of it are found all round the coast. It no doubt belongs 

 to an eruption of a date different from that which elevated the 

 Port du Moulin. 



After having observed the rocks in Serk I have no doubt that the 

 syenite is a part of the same stratified system with the hornblende 

 schist: and further that it has acquired its highly crystalline cha- 

 racter and lost more or less its bedded appearance by a process 

 which has failed to obliterate the stratification of the subjacent 

 schist, and therefore can hardly have been fusion or any near 

 approach to a fused state. There is no need to suppose even that 

 the syenite and schist have been exposed to any different circum- 

 stances, the latter is highly crystalline as well as the former, but 

 the former may have been originally deposited in a more homo- 

 geneous state. In the crystallizing action, as it goes on in substances 

 so solid as ordinary rocks, the transport of material from one part 

 of the mass to another can take place but very slowly indeed, so 

 that the complete obliteration of stratification in rocks formed of 

 alternating layers of different materials requires a very long time, 

 much longer than in rocks of which the successive layers were of 

 uniform or nearly uniform composition. 



The Serk beds give strong evidence in confirmation of the 

 view which I have previously taken of the metamorphic character 

 of the Guernsey syenite. 



In Jersey the granitic rocks have mainly determined the form 

 of the island. On the S. the masses projecting seaward are 

 granitic and between them the more easily disintegrated volcanic 

 ashes and trap, of which the central part of the island consists, 

 have been washed away, forming St Aubin's and St Brelade's 

 Bays. On. the N. the whole coast from a little W. of Fremont 

 Point to Grosnez Point is granitic. Between this and the syenite 

 of the Corbiere Point, St Ouen's Bay has been denuded out of 

 volcanic ashes and partly refilled with blown sand. On the E. 

 the projecting granitic boss of Mont Orgueil has protected the 

 land behind it, but the volcanic rocks have again been scooped out 

 in Grouville Bay. Fremont Point is a very tough trap, and the 

 whole of the N.E. projection of Rozel between Bouley Bay and 

 St Catharine's Bay consists of a hard conglomerate of rolled 

 pebbles, apparently an old sea-beach, cemented with volcanic 

 ashes. This resists weather well, and moreover dips seawards, 



