312 



MB. J. PARKINSON ON THE ROCKS OF [May I9OO, 



defined, of rounded speckly hornblendes with smaller ones between 

 them, making the whole of this area rather dark in colour. To this 

 succeeds a space characterized by larger but rounded hornblendes, 

 which in turn passes into a fine-grained mottled rock not identical 

 with the older one at the junction, but becoming closely similar 

 and indeed identical with it 2 inches or so farther on. There is a 

 slightly streaky look about this sometimes, as though the latter part 

 of the above change were not quite uniform. 



Locally at Le ISez the intrusive or veining rock becomes much 

 coarser. The quartz is not conspicuous to the naked eye, so that 

 two minerals only appear, namely, hornblende commonly in prisms 

 which are sometimes 1| inches long, at others in irregular patches; 

 and a matrix of yellowish-white felspar. 1 A thin section shows some 



Fig. 2. — Intrusive actinoh'tic rod- from near Le JS 7 ez. Jersey 



(about | nat. size). 



orthoclase, late in consolidation like the quartz, wedged in between 

 the other constituents. The difference in the degree of coarseness 

 is due to the hornblende, rather than to an increase in the size of 

 the plagioclases. The long prismatic hornblendes frequently 

 contain a felspar-centre, and in places crystals of the latter mineral 

 project into the former in an ophitic manner. This rock becomes 

 liner in grain through the rather rapid diminution in size of the 



1 Prof. A. de Lapparent regards this rock as a mere variation of the 

 ' epidiorite,' and he describes it as either a quartz-diorite or a hornblende- 

 granite, according to minor variations in mineral composition. The plagioclase 

 he defines as oligoclase. See ' Les Eoches <=ruptives de l'lle de Jersey ' Ann, 

 JSoe. Sci. Brux. vol. xvi, pt. ii (1892) p. 226 [sep. cops. p. 7J. 



