292 MB. W. E. WATT 01s THE GEOLOGY [June 1914, 



manuscript and examining the slides.^ To Dr. Herbert H. Thomas 

 I offer my best thanks for his help in identifying the rarer 

 minerals. To Dr. C. Gr. Cullis I desire to record my thanks for the 

 help which I have received in many discussions. At all times I 

 have derived great assistance from Prof. W. W. Watts, for whose 

 kindly interest and criticism I am deeply grateful. 



EXPLANATION OF PLATES XXXVIII-XL. 



Plate XXXVIII. 



Fig. 1. Contact-rock, first group, west of Ordbrae Crofts, magnified 30 

 diameters. The crystal showing cleavages in the centre of the field 

 is a plate of sillimanite. With it occur cordierite-grains, and it is 

 surrounded by grains of cordierite and pleonaste with some felspar. 

 Biotite and garnet are likewise present. (See p. 285.) 



2. Olivine-gabbro, Cairnford Bridge, magnified 30 diameters, nicols 



crossed. Olivine -crystals in the position of extinction are fringed 

 with fibrous amphibole, actinolite away from, and anthophyllite near, 

 the oh vine. At the centre of the lower portion of the photograph 

 is a plate of brown hornblende, which is found on the left as a third 

 zone round the olivine. Twinned plagioclase and pyrite are also 

 present. (See p. 273.) 



3. Cordierite -norite, Ladysmith, magnified 30 diameters. Here three 



plates of hypersthene are seen to contain inclusions of pleonaste and 

 magnetite, with also pyrite and cordierite. Round the pleonaste, 

 the cordierite, and the pyrite, a ring of colourless garnet occurs ; 

 while to the small pleonaste above the centre belongs a ring of 

 cordierite. Grains of cordierite and felspar make up the colourless 

 matrix. (See p. 291.) 



Plate XXXIX. 



Fig. 1. Cordierite-garnet-biotite rock, Ladysmith, magnified 30 diameters. 

 This, a further stage of the rock shown in PL XXXVIII, fig. 3, 

 exhibits pleonaste-grains with a pink mineral — garnet — surrounding 

 them. Biotite is also present, while the ground-mass is composed of 

 basic felspar and cordierite. 



2. Hornblende- andesine rock, Ladysmith, magnified 30 diameters. Com- 



posed of a plate of brown hornblende, poecilitically enclosing grains 

 of andesine. (See p. 281.) 



3. Cordierite-norite from Ladysmith, magnified 100 diameters, ordinary 



light. Shows vermicular garnet surrounding pleonaste and grains of 

 felspar. (See p. 291.) 



Plate XL. 



Geological map of the neighbourhood of Huntly, on the scale 

 of 1 inch to the mile, or 1 : 63,360. 



Discussion. 



Dr. J. V. Elsden drew attention to the great complexity of 

 the area described by the Author, and to its importance from a 

 petrographical point of view. There appeared to be in the 

 paper evidence bearing upon magmatic differentiation, marginal 

 differentiation, and composite intrusions. With regard to the last- 



