THE GEOLOGY OF THE ENGLISH CHANNEL. 129 



ducts, A few crystals appear zoned, some still show repeated twinning. 

 Much quartz, in which fluid inclusions are common; a majority of 

 these inclusions have bubbles. Brown mica. Apatite. Some iron- 

 staining. Quartz mica diorite. 



DIORITE 



M. 12d. S. 26° W. Edd., 17-8 miles. 



A striking looking rock by reason of the lustre of its constituent 

 minerals. Very dark in colour, consisting as it does of a black mineral 

 in prismatic form, and a clear felspar. Some of the little prisms of 

 the black mineral are as much as 3 mm. in length. 



The rock consists of a clear labradorite, in which, however, calcite 

 granules are developed here and there along cracks ; and a green 

 monoclinic pyroxene, segirine, in which a very marked schiller 

 structure has been set up, the microlites being of a dark brown. 

 Minute crystals of pyroxene appear in the felspars. Irregular patches 

 of an iron oxide, apparently magnetite, are common. 



M. 35b. S. 32° W. Edd., 18 miles. 



A fine grained, dark grey, granular rock with much mica. Besides 

 the dark mica there is obviously a lighter mineral, and the two are very 

 uniformly admixed. 



The section shows this rock to be a mica-diorite. Kich brown mica 

 occurs freely in irregular plates, and felspar in mosaic. A minority of 

 the felspar granules are striated, a very few show decomposition pro- 

 ducts. An occasional crystal of apatite is present and a fair amount of 

 titanic iron ore in small grains. The general appearance of the rock is 

 very fresh. 



A similar rock to M 35b. is 



M. 79a. S. 16° W. Edd., 48-7 miles. 



Dark grey, close textured, much mica in small form. 



M. 9s. S. 31° W. Edd., 217 miles. 



A dark coloured rock, the exterior of which shows large lustrous 

 black hornblende and dark drab and brown felspar. Fracture very un- 

 even and texture coarse. 



The felspars in this rock are now almost indistinguishable as such, an 

 occasional very small patch showing repeated twinning being all that 

 remains unaltered ; for the rest they have given place to a granular and 

 fibrous mineral of high refraction and double refraction, and apparently 

 colourless, although the larger grains may have a palest shade of green. 

 The rest of the slide is occupied by fibrous pale green hornblende. 

 Ilmenite is common. The structure ophitic. 



