part 4] PETROLOGY OF THE ARNAGE DISTRICT. 467 



are seen near East Kinharrachie, where they are veined by a few 

 acid strings composed of andesine and quartz. Farther north- 

 west the number of acid strings increases, and the hornblende- 

 schists appear in places to have mixed with the acid injections 

 along the walls of the vein-passages, with the result that the 

 threads hold considerable hornblende. Still farther north-west- 

 wards the veins broaden out and coalesce, and the rock assumes a 

 xenolithic aspect. The rounded xenoliths lie in a matrix of coarse 

 andesine, quartz, large hornblende-prisms, and biotite-plates. These 

 early stages may be seen in many excellent exposures lying 

 south-east of West Kinharrachie. At West Kinharrachie perhaps 

 half the rock is of later igneous parentage, with ' ghosts ' and 

 small rounded xenoliths of hornblende-rock hying in a felspathic 

 hornblendic mati-ix. In Craigouthorn Wood, north-west of West 

 Kinharrachie, the hornblendic mixtures pass into biotite-plagioclase- 

 quartz rocks resembling non-cordierite-bearing Arnage types. Still 

 farther north-westwards towards the Mill the dominant rock is of 

 Arnage Type, though here too are hornblendic lenticles. An 

 instructive but much weathered section is seen in an old quarry at 

 the roadside, 250 yards north of West Kinharrachie. Here the 

 hornblendic acid mixture with its hornblendic xenoliths appears 

 to have been engulfed as large blocks in the non-hornblendic, 

 biotitie, Arnage-T}q:>e rock, Avhich truncates the acid veins or 

 matrix of the hornblendic type. This points to the conclusion 

 that the acid veining supplies the loosening agent preparatory to 

 the advance of the main body of biotitie contaminated rock. 



In the details of their petrography the rock-tj^pes around 

 Kinharrachie are like those already described from the railway- 

 cutting (see fig. 4, p. 462). The hornblende occurs in the more 

 magmatic types in large ophitic plates enclosing euhedral felspars. 

 There is a Avell-marked fluxion in the more biotitie types. The 

 contact - metamorphism suffered bj the hornblende-schists is 

 described in § YI, p. 478. 



The rocks of the Kinharrachie area were described by J. S. Grant 

 Wilson 1 as ' brecciated gneiss ', and their outcrop was shown on 

 the 1-inch geological map. 



It has been demonstrated, therefore, that the result of contami- 

 nation of the initial magma by the Ellon hornblende-schists is the 

 production of rocks resembling quartz-diorites which, in places, 

 pass into granitic types. 



(D) Contaminated Rocks of the Ardletlien Area ; 

 the Ardletlien Type. 



Now that the characters and origins of the contaminated rocks 

 of Arnage and Kinharrachie Types have been discussed, the more 

 intricate ground around Ardletlien (see fig. 5) may be considered. 

 The area dealt with here comprises the Ardlethen estate south of 



1 ' Explanation of Sheet 87 ' Mem. Geol. Siirv. Scot. 1886, p. S. 



