part 4] PETROLOG-Y OF THE AEXAGE DISTRICT. 465 



(C) Hornblende-Biotite-Quartz-Plagioclase-Rock, or 

 the Kinharrachie Type. 



The second of the main types of contaminated rock is dioritic in 

 composition, and is found between the Little Arnage kernel and 

 the Ythan (see fig. 5, p. 468). Two series of exposures serve to 

 explain the origin of this type : the first of these is supplied by 

 the railway-cutting between Ellon and the Little Arnage kernel, 

 supplemented by abundant rock-knobs in the ground due west 

 of the railway towards Waulkmill ; the second is provided by 

 numerous outcrops in the woods between the Ellon-Methlick main 

 road and the Ythan (see fig. 5). These two series of exposures 

 are described in detail. 



The railway-cutting in the rocks concerned begins at a point 

 half a mile north of Ellon Station, and continues northwards for 

 over a mile until the norite of the Little Arnage kernel is reached. 

 A traverse from south to north along the cutting displays the 

 characters and origin of this dioritic type very clearly. In the 

 cutting due east of Mains of Auchterellon are found coarse 

 hornblende-schists and subordinate biotite-gneisses of the Ellon 

 Series ; these schists are threaded with delicate strings of acid 

 igneous material. The same association of country-rocks continues 

 for three-quarters of a mile northwards along the cutting ; but an 

 increase in the amount of igneous material can be observed. At 

 the road-bridge half a mile south of Little Arnage the blocks 

 blasted from the cutting are piled up in a field on the west 

 side of the railway, north of the road, and supply very clear 

 evidence as to the nature of the rocks concerned. Country-rock 

 still dominates, but a good deal of igneous veining is seen, and 

 noteworthy is the presence of abundant garnets in both veins and 

 host. Some hundred yards north of the bridge the rock definitely 

 becomes mainly igneous, with hornfelsed xenolithic fragments of 

 hornblende- and biotite-schists ; northwards the amount of the 

 igneous component increases, until the true norite of the Little 

 Arnage kernel is reached. An exactly similar gradual passage 

 from country-rock to contaminated rock can be seen in numerous 

 traverses from the Ellon-Kinharrachie road, north-westwards to 

 Waulkmill and Little Arnage. In the conspicuous knob between 

 Hayhillock and Waulkmill the dioritic type is found in intimate 

 association with rocks of the Arnage Type already described. 



In hand-specimens the contaminated rock, largely of igneous 

 origin, is usually coarse in grain and speckled with white felspars 

 and black biotites and hornblendes ; often the rock is homogeneous 

 and of normal igneous aspect, but sometimes dark hornblendic or 

 biotitic streaks, representing relic xenoliths, are visible. In many 

 cases it would be an easy matter to conclude, from an inspection of 

 hand-specimens alone and without field-knowledge, that the rocks 

 under discussion should be regarded as true igneous rocks. 



The minei'al-eontent of this dioritic type is quartz, plagiocla.se, 

 hornblende, biotite, pyroxene, and iron-oxide. 



