■iQQ ME. II. H. READ OX THE [vol. lxxix, 



The quartz occurs mainly in lenticular areas made up of 

 elongated grains, which usually show a slight undulose extinction. 

 The felspar is a medium andesine, with a refractive index of 

 1;553, and forms stout ciystals somewhat lenticular in outline. 

 Fine albite and pericline twinning is developed. A few crystals of 

 orthoclase have been noted. Biotite forms trains of small 

 plates expressing the fluxion, or large individual plates ; the 

 pleochroism is from pale yellow to deep brown. Hornblende 

 occurs in two types : the one forms collections of prisms, almost 

 colourless in slice and exhibiting lamellar twinning, the other builds 

 very large ophitic plates enclosing the felspar. This second 

 variety is deeply coloured, and is pleochroic in yellow, green, and 

 brown. Both varieties are usually found associated, but their 

 time-relations are uncertain. Small areas of quartz-hornblende 

 micropegmatite. akin to those resulting from reaction-processes, 

 have been noted. Both monoclinic and rhombic pyroxenes 

 occur. The monoclinic p} r roxene is found only as rounded grains, 

 associated with quartz and enclosed in large hornblende-plates ; it 

 is possibly of contact-origin (see p. 478). Hypersthene is rare ; 

 it occurs in subhedral grains showing vivid green and pink pleo- 

 chroism, and is often associated with hornblende and biotite. Black 

 iron -oxide forms grains in the mafic minerals, or scattered dirty 

 particles (chiefly in the pale amphibole). 



The relative amounts of hornblende and biotite vary, sometimes 

 only a little hornblende being seen, at others only a little biotite ; 

 but usually about equal amounts of each occur. 



These rocks show, especially in the biotite-rich tj'pes. a well- 

 developed rluxional structure, made plain by the lenticular form 

 assumed by the quartz and felspar and by the rude alignment of 

 biotite-plates. 



It is of importance to record that, in certain places at the 

 northern end of the cutting described, the contaminated rock is 

 richer in leucocratic minerals than usual, and approaches a horn- 

 blende-granite in appearance. The constituent minerals of this 

 granitic type are dominant oligoclase-andesine, less common 

 orthoclase and microcline, with biotite and hornblende, and the 

 rock occurs as schlieren in the dioritic type. 



The second series of exposures of contaminated rocks of Kin- 

 harrachie Type is found around West Kinharrachie, and can be 

 easily studied in the wooded knolls lying between the Ellon- 

 Methlick road and the River Ythan (see fig. 5, p. 468). There is 

 here a very complete passage from hornblende-schists of the Ellon 

 Series north-westwards into biotite- and hornblende-bearing con- 

 taminated rocks of dioritic aspect. Certain of the mixed rocks are 

 richer in biotite, felspars, and quartz, and poorer in hornblende 

 than the usual dioritic rock ; they provide a hornblende-granitic 



The biotite-o-neisses and hornblende-schists of the Ellon Series 



