128 Prof. Liveing, On the rocks of the Channel Islands. [Nov. 14, 



with the granite at the junction. This however is not the case ; 

 the junction is sharply defined and in the cliff the felspathic rock has 

 weathered away for some distance leaving a clean wall of granite. 

 On the W. side where the junction occurs between the granite 

 and stratified ashes, seen about half a mile from L'Etacq on the 

 St Ouen's road, the ashes rest on what looks to me like an eroded 

 surface of granite. The ashes may however be of a different date 

 from the rock of Fremont Point, though I see no ground for 

 thinking that there can be much difference of date, as the Fremont 

 Point rocks are evidently part of one system with the other rocks 

 of Bonne Nuit Bay, which are continuous with those in the 

 interior of the island. I rest my conclusion however, as to the 

 greater antiquity of the granite on another ground, which is, that 

 the granite is intersected by many dykes, mostly greenstone, 

 while I have not detected a single greenstone dyke, only one 

 or two dykes of any kind, in the ashes and trap which form 

 the central part of the island. The rocks of Fort Regent and 

 Greve d'Azette before mentioned are as full of dykes as the 

 granite but are disconnected by their mineral characters from 

 the system of volcanic rocks of the interior of the island. I 

 conclude therefore that these rocks, as well as the granitic, are of 

 older date than the intrusion of the dykes, but the volcanic rocks 

 of the rest of the island newer. If that is so, we must look to 

 some cause other than igneous fusion for filling the veins. In 

 this connection it is worth notice that in most cases, all that I 

 have ever examined, the materials which fill branching veins 

 of granite differ somewhat from those of the mass from which 

 they appear to be derived ; generally they are more quartzose, and 

 I have, in my former paper, noticed the peculiarity in the arrange- 

 ment of the felspar crystals in some of them. If these Jersey 

 veins had been purely quartz veins they would be set down 

 at once as results of segregation from the adjoining rocks, and 

 if they had been purely felspathic, occurring as they do in a 

 felspathic rock, they would be common occurrences assigned to a 

 similar cause. In this case we have a mixture of quartz and 

 felspar in which the quartz predominates and is coloured red 

 with oxide of iron like the adjoining granite, and there is no 

 reason to assume 'that any different agency has been at work 

 in producing it, from those which produce ordinary quartz and 

 felspar veins. It is worth notice that the porphyritic crystals of 

 felspar in the trap rock are also coloured red for a short distance 

 from the granite ; and in Guernsey I have seen, near Cobo, a 

 vein of red felspar passing right across a dark coloured greenstone 

 dyke from wall to wall of red granite, where the granite seems at 

 least to have supplied the colouring,' matter if not the mass of the 

 vein. It must not be supposed that I deny the possibility of 



