49 



taken place in the paste, but no orthoclase could be detected. 



It seems as though advancing metamorphism has tended to 

 produce evenness of grainsize along with recrystallization in 

 the rocks affected. 



The absence of orthoclase in this rock may possibly be 

 due to its having become embedded in the granite at a late 

 stage in the cooling history of the latter, when little or no 

 exchange of material was possible. 



(3) CONTACT METAMORPHISM AT ROSETTA HEAD. 



It is impossible wholly to differentiate the effects of the 

 granite from those of the syenite, but in certain respects the 

 special influence of the latter can be clearly discerned. 



The approach to the igneous rock from the landward side 

 is across the strike of the schists, and as the orig^" lal sediments 

 probably varied somewhat both in texture an I in chemical 

 composition the study of the progressive metamorphism is to 

 some extent interfered with. 



In some cases special metamorphic minerals have been 

 produced, such as andalusite and cordierite, while the 

 emanation of magmatic solutions, connected particularly 

 with the syenite, has resulted in the introduction into the 

 invaded rocks of such minerals as albite, rutile, apatite, and 

 zircon, and in the alteration of biotite and chlorite. 



Tlie impregnation appears to have been selective, or rather 

 the solutions have not spread out uniformly from the con- 

 tact, but have perhaps followed the beds of greatest permea- 

 bility, and consequently one finds occasionally among the 

 impregnated rocks some which have simply been recrystallized 

 without noticeable addition of material. 



(a) Andalusite Mica Schists. — A specimen from near the 

 contact on the western side of Rosetta Head is seen to be 

 micaceous and to have a definite schistosity, very slightly 

 waved, and roughened by knots. 



In thin sections the minerals present comprise quartz, 

 biotite, andalusite, chlorite, muscovite, and iron ore, with 

 fairly plentiful little zircons showing pleochroic haloes, and 

 sometimes coronae as well, embedded in the biotite and chlor- 

 ite; felspar appears to be absent. Chlorite is associated and 

 intergrown with biotite and evidently derived from it, but its 

 distribution seems purely haphazard. The mineral has the 

 peculiar characters of the chlorite in the albite syenite; its 

 R.I. is a trifle high for ordinary chlorite, and it is uniaxial 

 and positive. The colour is a very pale green with slight 

 pleochroism. Birefringence is distinctly weaker than that of 

 quartz and extinction from the basal cleavage is slightly 

 oblique revealing multiple twinning parallel to the base. The 



