Vol. 6S.] PETEOLOGICAL NOTES ON GUEENSEY, ETC. 35 



of biotite, as if that were in some way derived from it. Acicular 

 prolongations of the green hornblende suggest a slight secondary 

 growth. Grains and granules of iron-oxide are present ; but 

 apatite is inconspicuous, and sphene probably absent. Thus the 

 rock, notwithstanding its aspect in the field, is only rather a basic 

 diorite. 



Ten slices have been cut from specimens of diorite collected 

 during oar late visit ; and those described in 1884 ^ have been 

 again examined. As a minute description of the microscopic details 

 would unduly lengthen this paper and have no general interest, 

 we shall confine ourselves to indicating the more characteristic 

 features of the chief varieties. 



A specimen of ' birdseye ' from Hougue a la Perre, slightly more 

 felspathic than the one previously described, contains hornblende, 

 brown and green, some of which, if not all, has been formed by 

 paramorphic change from a very pale-brown augite. The larger 

 grains are rather irregular in outline and studded with small 

 crystals of felspar, which cause the conspicuously poecilitic aspect 

 of the larger hornblendes in this rock. Their extinction-angles, 

 and those of the felspar in the body of the rock, suggest labradorite 

 or in some cases andesine. 



A specimen from the Bouet quarry, dark in colour, with its 

 hornblendes tending to be parallel ('long grain'), shows thatmineral 

 to be the more abundant (see PI. I, fig. 1). It is of a rich brown 

 tint, and associated with a little pale brownish-grey augite, from 

 which it probably has been formed ; the felspar is hypidio- 

 morphic, and similar to that in the last-named rock ; a little quartz 

 is present. 



A dark, rather fine-grained variety, cutting ' birdseye,' as de- 

 scribed, at Hougue a la Perre, shows a tendency to porphyritic 

 structure in the hornblende, which is more abundant than the 

 felspar, and has its larger crystals spotted with that mineral. A 

 little brownish augite may be seen in process of conversion into 

 hornblende, and a grain or two of free quartz. (See PI. 1, fig. 2.) 



A specimen from one of the light-coloured veins, near Hougue 

 a la Perre, consists largely of felspar. This is in bad preservation, 

 but most of it is plagioclase, though some orthoclase may also be 

 present. The ferromagnesian constituent is small, irregular in 

 outline, and often occurs in tiny groups, suggestive of chloritized 

 biotite rather than of hornblende. With this is associated a 

 colourless or faintly yellow material, with fairly-high refractive 

 index and bright polarization-tints, probably epidote. A little iron- 

 oxide is visible, but neither quartz, nor sphene, nor apatite. 



The diorites of Fermain Bay and Castle Cornet, both of normal 

 kind, were described in 1884, and we have again examined the 

 slice — besides a new section from the former, and one showing 

 the ' birdseye ' type from the latter place ; but, as all are in poor 

 preservation, they do not call for special notice. 



' Q. J. G. S. vol. xl, p. 425. 



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