Vol. 70.] OF THE COUNTRY ABOUND HUNTLY. 291 



between the Indian and the Scottish types in regard to the formation 

 of garnet at the expense of hypersthene. 



In the rock from La dysmith, the hypersthene contained inclusions 

 of pleonaste and magnetite. Hound both these spinellids, and 

 separating them from the hypersthene, is a zone of colourless 

 mineral (see PL XXXVIII, fig. 3). Usually this is isotropic, 

 and has a high refractive index, when it is a colourless garnet ; 

 but sometimes its refractive index and birefringence agree with 

 those of the cordierite of the rock. 



The colourless garnet showed here also its vermicular markings, 

 which interlocked with greenish outgrowths of the spinel. At this 

 point there would seem to be an intergrowth of spinel and garnet. 

 In the monograph on ' The Charnockite Series,' 1 Sir Thomas 

 Holland records a case where the pleonaste is surrounded by a zone 

 of pale-pink, highly-refracting, isotropic mineral, ' presumably the 

 ordinary magnesia-alumina spinel.' However that may be, it is 

 clear that, in this case also, the hypersthene is being broken up, 

 though in a somewhat different way. 



V. Conclusions. 



The conclusions arrived at in the foregoing pages may be briefly 

 summarized as follows : — 



(1) Two separate series of igneous rocks are to be distinguished, 

 a foliated and a non -foliated series. 



(2) The non-foliated series shows signs of movement during 

 injection and consolidation in the prevalence of fluxion-banding 

 and mortel-struktur. 



(3) The non-foliated series contains in itself types of different 

 ages and varied composition. 



(4) The later types alter the earlier (non-inflated) norites at 

 their contact with them, with the production of cordierite-norites. 



(o) Cordierite-norites are likewise produced in the intrusive 

 rocks by the absorption of material, mainly alumina and magnesia, 

 from the adjacent crystalline rocks — here phyllites more or less 

 homfelsed. 



(6) The cordierite-norite, by the destruction of its cordierite and 

 hypersthene, tends to pass into a rock composed of garnet, labra- 

 dorite, and biotite. 



(7) The destruction of the hypersthene and the formation, with 

 the help of the felspar, of pleonaste, garnet, cordierite, and 

 magnetite, may be noted at various stages. 



This research has been carried out at the Imperial College of 

 Science & Technology with the help of a scholarship granted by 

 the Carnegie Trustees for the Universities of Scotland. To 

 Dr. J. S. Flett I am indebted, not only for constant advice, but 

 for the personal labour that he has undertaken in reading the 



1 Mem. Geol. Suxy. India, vol. xxviii (1900) p. 168. 



