470 MR. H. II. BEAD OK THE [vol. lxxix, 



respectively west-north-west of Glencroft. The dips of the 

 bedding in all these roof-cakes are the same. Not much different 

 are the dips of the bedding in the smaller xenoliths in the ground 

 near Ardlethen and out towards Ythsie. These are roof -phenomena. 



The diorite or hornblende-biotite-felspar-quartz-rock of Kinhar- 

 rachie Type is simply the southern continuation of that type from 

 the north side of the Ythan (fig. 5). Such types occur in Boat 

 Wood, 200 yards west of Boat of Ardlethen, in the wood 400 yards 

 west of Hillhead of Ardlethen, and in the roadside quarry 340 

 yards south-south-east of Ardlethen. West of Boat Wood this 

 type is of subordinate importance, and occurs only as patches 

 in rocks of Arnage or Ardlethen types. In slice, rocks of the 

 diorite type show coarse associations of quartz, oligoelase-andesine 

 and andesine, large plates of biotite, and ophitic hornblende-plates. 



Occasionally, as in the wood 1000 yards north of Ardlethen, 

 the contaminated rocks are hypersthene-bearing. They are com- 

 posed of hypersthene, hornblende, biotite, quartz, and an inter- 

 mediate plagioclase ; they are to be compared with the Gabbro 

 Type discussed on p. 458. 



The Ardlethen Type occurs in three areas north and south of 

 Ardlethen (fig. 5, p. 468). The structural relations of this type 

 to the rocks just described will be best discussed by considering 

 certain of the localities at which they are well seen. In fig. 5 

 these localities are shown by numerals : fluxion in these and the 

 adjacent rocks is indicated also in the figure. 



Locality 1. — 400 yards south-west of Hillhead of 

 Ardlethen. — This is a poor exposure, but sufficient is seen to 

 provide an introduction to the problem. Rock of Ardlethen Type 

 is here intimately associated with cordierite-biotite-oligoclase- 

 quartz-rock of Arnage Type ; the whole is strealvy, fluxional, and 

 xenolithic, variable in grain and in distribution of biotite, which 

 occurs often in felts in the more acid rocks. A variation from 

 Ardlethen Type to Arnage Type is often seen in the same block. 

 The inference can be drawn that here the granitic end-product 

 occurs as lenticles and streaks in the dominant cordierite-bearing 

 Arnage Type, and, like it, must be considered to be of contaminated 

 origin. 



Localit}" 2. — In the wood, south of the Yowlie Burn, 

 300 yards north-west of Hillhead of Ardlethen. — At a 

 point 100 yards south of the Yowlie Burn are seen magnificent 

 crags of garnetiferous cordierite-contaminated rocks of Arnage 

 Type, with abundant blue hornf els-xenoliths ; a good flow-structure 

 strikes north 15° west. Northwards from this locality we en- 

 counter a perfect and gradual passage from these Arnage Type 

 rocks with abundant xenoliths into more felspathic types with 

 fewer xenoliths, and from these again into a gneissose granitic 

 Ardlethen Type, with no xenoliths beyond a few streaks of 

 aggregated biotite of the thickness of cardboard. The whole 



