part 4] petrology or the arnage district. 473 



laths or stouter plates wrapping round the felspars. In some 

 examples the biotite is abundant, forming a felt pricked through by 

 small felspars and quartzes. There are, too, streaks richer in 

 biotite than the normal rock, which probably represent relics of 

 xenoliths of biotite-schist. 



The minerals just described constitute the usual Ardle then Type 

 (see fig. 4, p. 462) ; there remain, however, certain minerals of 

 some importance to be noted. Garnet in rounded pinkish grains 

 is widespread, though not abundant. Spinel occurs in clusters 

 and streaks associated with cordierite ; these undoubtedly 

 represent far-gone xenoliths of argillaceous composition. The 

 occurrence of these minerals characteristic of the definitely 

 contaminated rocks adds strength to the view that the Ardlethen 

 granitic type is of contaminated origin. 



The rock seen in Glencroft Quarry is a granite with only a 

 poorly-developed fluxion. It is composed of biotite, the felspars 

 of the Ardlethen Type, and quartz. Here, too, may be noted a 

 tendency for the biotites to be clustered into rude streaks. 



An average rock of Ardlethen Type has been analysed by 

 Mr. E. G. Itadley; this analysis is set forth in Table III, p. 464. 



VI. The Xenoliths and Horneelses. 



The two series of Highland Schists taking part in the contami- 

 nation of the initial magma provide recognizable xenoliths in the 

 contaminated rocks ; these xenoliths give examples of exceptionally 

 beautiful hornfelses, and, moi'eover, they play, or their like have 

 played, a very important part in the contamination-process. No 

 definite aureole has been found around the Arnage Mass, and 

 such is not to be expected, considering the gradual passage from 

 country-rock to contaminated rock that is everywhere encountered. 



The broad distributions of the xenoliths belonging to the two 

 main rock-series — the Fyvie and the Ellon Series — are shown in 

 fig. 2 (p. 452). It has been pointed out, also, in the description of 

 the contaminated rocks, that the Arnage and Kinharrachie Types 

 carry xenoliths of argillaceous schists of the Ellon and Fyvie Series 

 and hornblende-schists of the Ellon Series respectively. The reader 

 may thus form some notion of the distribution of the different 

 types of xenoliths. With regard to the number of xenoliths, it 

 may be stated that they must be reckoned in hundreds of thousands 

 in contaminated rocks of Kinharrachie and Arnage Type ; but 

 they are rare in the Ardlethen granitic type, and only one has 

 been noted in the norite of the kernels. 



Four types of xenoliths are met with, corresponding to the 

 original rock-types of (1) felspathic quartzite of the Fyvie Series, 

 (2) andalusite-schist of the Fyvie Series, (3) biotite-schist of the 

 Ellon Series, and (4) hornblende-schist of the Ellon Series. 



Some of the multitudinous details noted of the mode of occur- 

 rence of the xenoliths may lie given. The strike and dip of the 

 bedding of the larger xenoliths agree with those of the adjacent 



2 k2 



