1877.] of the r odes of the Channel Islands. 83 



intruded mass, but this cannot be, for in the first place the fusion 

 would have produced an incorporation of the vein with the beds at 

 the junction, which is not the case; and in the next place would 

 have produced a uniform arrangement of the crystals in the beds, 

 instead of which the beds have a different texture in the middle 

 from that which they have at their upper and lower surfaces where 

 they come in contact with the hornblende rock. The surfaces of 

 the beds where they are in contact with the hornblende rock 

 (which is quite unaifected but must have been subject to the same 

 temperature) are not composed of the same material as the interior, 

 but consist only of felspar and quartz, i. e. of felspar crystals with 

 grains of quartz in them. The fact is that the vein, by affording 

 easier communication both upwards and downwards, has contri- 

 buted the conditions requisite for the crystallization of these beds, 

 that is the freer permeation of air, water, steam and other sub- 

 stances, and concotnitant variations of temperature. 



In Alderney the lower strata are grey syenites closely resembling 

 those of Guernsey, but overlaid by a stratified sandstone, consisting 

 of felspar and quartz. It has probably been a loamy sand origin- 

 ally, and the particles of quartz in it look like original particles of 

 sand, but the felspar is so highly crystalline that it must be called 

 a metamorphic rock. 



In Jersey the metamorphism of the rocks is quite as remark- 

 able, but of a different kind. I have been unable to trace the con- 

 nexion of the Jersey syenite, which is very different from that of 

 the more northerly islands, with any stratified rocks. Ansted 

 asserts that it may be done, but I had not time to explore the 

 whole island. The Jersey syenites contain a large proportion of 

 felspar, a variable proportion of quartz, and but little hornblende, 

 and are generally coarsely crystalline, but in places pass into a very 

 fine grained highly quartzose rock, or into a fine grained mixture 

 of felspar and quartz, with larger crystals of felspar and lumps of 

 quartz interspersed in a porphyritic manner, looking very much 

 like a Cornish Elvan. This rock seems to form a sort of bed in 

 the coarse syenite at St Brelade's, for it passes under the coarse 

 syenite on the east side of the bay and above it on the west side. 

 It is perhaps worthy of remark that in the processes of metamor- 

 phosis by which these and many other rocks have acquired either 

 a porphyritic or syenitic structure the quartz does not assume 

 the external form of crystals. It acts on polarized light as a 

 crystal, but its external form is usually more or less rounded and 

 granular, or looking as if it were pseudomorphic, as seen in section. 

 This character is independent of the size of the crystals. In the 

 coarsely crystalline parts of the syenite near St Brelade's, where the 

 segregation of the felspar and quartz has been carried to the far- 

 thest extent, the quartz still appears in more or less rounded 



