298 miss c; a : . kaisin on • [May. 1903, 



represented in one or two crystals. One or twa others, rounded in 

 outline, apparently without cleavage, containing minute fluid enclo- 

 sures, exhibit an all-round extinction. This suggested the possibility 

 of leucite, but the characteristic structure is wanting, and the grains 

 might be transverse sections of a hexagonal crystal like nepheline. 

 The porphyritic crystals sometimes enclose grains of augite or patches 

 of the groundmass. The groundmass is micro-ophitic, perhaps with a 

 little residual glass, with lath-shaped felspars often singly twinned, 

 and nepheline in rectangular and hexagonal sections. A pale filmy 

 hornblende exhibits characteristic cleavage, especially well shown 

 in one crystal. The pleochroism in this (and in one or two which 

 extinguish at about 40°, and enclose opaque blackish grains) is 

 from pale chestnut or reddish-brown to very pale fawn-colour. Iri 

 other (mostly minute) crystals, often extinguishing at 18° or 20°, 

 it is from chestnut-brown to pale apple-green. The hornblende may 

 be a common species, but it exhibits a resemblance to the catophorite 

 of Brqegger from Grussletteu. 1 Dark-brown or red-brown crystals^ 

 often opaque in the centre, are possibly cossyrite. 2 Another 

 mineral, having a peculiar pleochroism to a deep greenish-blue, 

 often occurs in a small patch clustered around nepheline or felspar, 

 and although perhaps not the most typical, example, is doubtless 

 riebeckite, 3 possibly with some segirine, and the slice contains a 

 pale-green augite. 



A rock obtained just before reaching Bilo, dark-grey, with a 

 somewhat greasy lustre, shows a slight linear streaking. The 

 small, crowded, colourless crystals in the groundmass are mostly 

 nepheline, exhibiting hexagonal and rectangular sections. Some 

 microchemical tests gave further corroboration of the identification 

 of this mineral. The rock -slice was readily etched by hydrochloric 

 acid (in 1| minutes), and stained with malachite-green. The 

 sol ution in hydrochloric acid deposited many small cubes of sodium- 

 chloride, and in hydrofluosilicic acid, good crystals of sodium-nuo- 

 silicate. Lath-shaped felspars, less sharply defined, and a small 

 pyroxene occur, resembling minerals found in the next-described 

 rock. Pale-brown films, sometimes hexagonal, with aggregate 

 polarization, are possibly mica. 



A speckled greyish rock from Bilo exhibits close wavy shimmering 

 surfaces. In the microscope-slice, two generations of felspar- 

 crystals occur, both numerous, distinctly orientated, probably 

 sauidine and anorthoclase, the latter often exhibiting an undulose 

 extinction, both in this and in the preceding rock. Some of the 



1 See ' Die Eruptivgesteine des Kristianiagebietes : I. Die Gesteine der 

 Grorudit-Tinguait Serie,' Vidensk. Skrift. 1894, No. 4, pp. 27-39; and 

 Kosenbuseh [tran si. Iddings] ' Microscop. Physiogr.' 4th ed. (1898) App. 

 p. 352 c. 



2 This identification was suggested by Mr. G. T. Prior. I have to thank 

 Mr. L. Fletcher for kind permission to study slices in the collection at the 

 .British Museum (Natural History). I owe many thanks to Mr. Prior for 

 selecting some of these, for looking at my slides, and for giving me on 

 several a confirmatory opinion. 



3 I have to thank Prof. Bonney for the loan of slides in which I was able to 

 study typical riebeckite, some in the Mynydd-Mawr rock, and a still richer 

 development in a Socotra specimen. 



