THE GEOLOGY OF THE ENGLISH CHANNEL. 143 



M. 9d. 



A rather light grey rock, which appears to be a compact and very 

 fine-grained grit ; looks much like many grits of the Devonian age. 



The microscope confirms preliminary examination ; this rock is a 

 grit of close texture. A considerable proportion of the granules are 

 felspar, many showing repeated twins. 



A number of the grains prove to be of compound structure, and are 

 portions of quartz and felspar mosaics from some original schist or 

 gneiss. Further than this, three of the larger grains are compounded 

 of portions of felspars with bent striation and portions of quartz 

 mosaic, being, in fact, derived microscopic specimens of gneiss. As 

 bearing on the age of the rocks which have supplied the fragments, 

 this slide is distinctly interesting. The interstitial matter largely con- 

 sists of a rather pale chlorite in which occur rare blades of pale mica, 

 There is some ilmenite, apparently detrital. (Plate YIII, figs. 1 and 2 ) 



M. llf. S. 26° W. Edd., 17-8 miles. 



A fine grey grit slightly browned by exposure. Much like last in 

 general appearance, and may well be of Devonian formation, already 

 included as quartzite, the cement being apparently silica. The grains 

 are sub-angular and include a few felspars. There are rather 

 numerous grains of sphene, some irregular, some of the characteristic 

 lozenge shape, all apparently derived. 



Grits, not microscopically examined, were also taken at M. 31, M. 27, 

 M. 26, M. 14, M. 20, M. 16, M. 9, M. 40, M. 19, M. 41, M. 77, and M. 80. 

 SLATES. 



Unaltered slate was scarce, as might be expected from the fact that 

 it would usually be associated with much harder material, and probably 

 be soon destroyed. 



M. 77a. S. 11° W. Edd., 38-8 miles. 



Dark compact shale, a clay slate. 



Under the microscope appears built up of minute grains of high 

 double refraction. There are frequent traces of minute organisms, 

 some possiljly foraminifera. Some shell fragments still consist of car- 

 bonate of lime, and numerous forms of circular section are infilled with 

 calcite. 

 M. 39. S. 38" W. Edd., 219 miles. 



A decomposed slate. 



ALTERED SLATES. 



354/4J. 6^ miles W. from Rame Head. 



A slate of Devonian type, evidently altered by the proximity of the 

 andesite dyke which here occurs. 



