478 MB. H. H. BEAD OK THE [vol. lxxix, 



of which is set forth on p. 477, shows in slice perhaps 97 per cent. 

 of cordierite, some spinel, a few plates of biotite, and scarce 

 plagioclase-grains — it is almost a cordierite-rock. The analysis 

 reveals an unexpectedly large amount of iron-oxides. It seems 

 that, in the cordierite of this rock, iron-oxides replace much of the 

 alumina and magnesia of normal cordierite. Other hornfelses of 

 this type are rich in sillimanite. 



A second type of hornfelses of this class is richer in quartz, 

 and bears biotite and garnet : this type tends to be banded. 

 A variant is the hypersthene-hornfels which, in addition to the 

 minerals just noted, has certain bands rich in grains of hyper- 

 sthene. 



Biotite-schist.— Hornfelsed biotite-schists of the Ellon Series 

 are coarsely-banded rocks made up of varying associations of 

 cordierite, biotite, quartz, plagioclase, spinel, garnet, and silli- 

 manite. These ingredients are arranged in rude bands dominated 

 by certain minerals. The two chief types of bands are composed 

 of cordierite, spinel, and sillimanite. and of garnet, biotite, quartz, 

 and plagioclase respectively. Cordierite forms irregular grains 

 collected into lenticles or bands ; pleochroic haloes are magnificently 

 developed, and there are some sector-trillings ; occasionally, inter- 

 growths with quartz have been noted. Spinel is so extremeby 

 abundant that green bands appear in the slice ; it forms irregular 

 grains of a deep-green colour and clustered in cordierite bands; it is 

 not found near garnet (see fig. 6, p. 476). Sillimanite is not 

 abundant, and occurs as colourless prisms or needles in cordierite- 

 and spinel-layers. Garnet builds large pink grains, sometimes 

 spongy and with biotite-plates arranged in ocellar fashion around 

 them. The biotite is pleochroic from pale yellow to deep red, 

 and occurs as small plates in the cordierite-spinel bands and large 

 plates in the biotite-rich bands. Quartz-grains, acid plagio- 

 elase-grains, and magnetite complete the rock. 



Horn blende -schist. — The hornblende-schist of the Ellon 

 Series occurring in the contaminated rocks is usualby richer in 

 biotite than the normal hornblende-schist. There is a more or less 

 marked tendency for both hornblende and biotite to form very 

 large plates sieved through by quartz and plagioclase, or to form, 

 as it were, a cement to these minerals. In certain xenoliths taken 

 out of the contaminated rocks of Craigouthorn Wood, north of 

 West Kinharrachie, the rock is composed of masses of pale 

 poikiloblastic hornblendes enclosing small rounded plagioclases 

 and quartzes. 



Another result of contact-metamorphism of the hornblende- 

 schists is the formation of pyroxene. The normal hornblende- 

 felspar rock is interrupted by small rounded patches consisting of 

 an intergrowth of hypersthene with plagioclase and magnetite, the 

 last often forming central threads to the ramifying hypersthenes. 

 In other cases the newly-formed hypersthene builds stout crystals 

 replacing portions of the hornblende. 



