128 G. D. OSBOKNE. 



of pressure and resulting solution and deposition. Harker, 1 

 however, in connection with his work on the British Ter- 

 tiary terranes, disagreed with Judd's view, and hinted at 

 the structure being a primary one. Judd would certainly 

 extend the idea of schillerisation to wide limits, thereby 

 dealing with changes in felspars and olivines. Zirkel, 2 too, 

 mentions the process in connection with the mineral olivine. 



Without discussing the matter definitely, the opinion 

 may be stated that the occurrence of these inclusions in 

 the Basin rocks is indicative probably of separation from 

 solid solution in the host rather than of infiltration and 

 solvent action. Tin's would not accord with Judd's view, 

 but would postulate a secondary nature, in that the sepa- 

 ration of the inclusions took place after the actual crystal- 

 lisation of the host. This tentative conclusion is based on 

 the examination of the schillerised minerals, with special 

 reference to their association, to the changes in adjacent 

 felspars,. and to the occurrence of the rocks containing them. 



This mode of origin of the dark plates is therefore surely 

 analogous to the secondary pertliitisation of alkali-felspar, 

 the albitic element often originally held up in potash- 

 felspars corresponding to the metallic oxides which existed 

 in solid solution in the pyroxene. It would appear that 

 the pyroxene individuals have been, with reference to the 

 metallic constituent, in a labile condition, but while the 

 dominant factor regulating the spontaneous separation of 

 the dark inclusions has been that of decreasing temperature, 

 still in the present study the possibility of pressure aiding 

 in a small way in their development has been recognised. 



One rock which is included in this group is of the nature 

 of a hyperite, containing both monoclinic and orthorhombic 

 pyroxenes and much olivine together with a little primary 



1 Barker, " Tertiary Igneous Rocks of Skye," p. 109. 

 3 Zeitschr. der deutsch. Gesell. (1871) p. 189. 



