440 Pro/1 Dr. T. G. Bonney — Troktolite, etc., in Aberdeenshire. 



I believe that I visited the same locality, though I could only find 

 one quarry in serpentine (very probably two excavations have now- 

 been worked into ore). The locality is about eight miles from the 

 town of Aberdeen, and a short distance to the east of the high road to 

 Tarves.^ The quarry is close to a branch road and is visible from the 

 main one. I was told that the name of a farmhouse, which stands 

 on the ridge, a short distance north of the quarry, is Overhill, This 

 ridge is a conspicuous feature, running for a considerable distance 

 roughly parallel to the road, as the above-mentioned quarry is ap- 

 proached. It is no doubt a portion of the "ridge of dark trap," 

 which is mentioned in the Ordnance Gazetteer of Scotland as 

 " starting from the Black Dog's mouth, and running through the 

 entire parish of Belhelvie, from four to six furlongs wide, . . . flanked 

 at one point by serpentine." 



The outcrop of serpentine is but a small one, for it does not appear 

 to extend much beyond the limits of the pit. The ridge here, and 

 doubtless elsewhei'e, mainly consists of a rock of rather variable 

 coarseness, which much resembles the well-known troktolite (or 

 forellenstein), of Volpersdorf. This similarity struck me at once in 

 the field, and is fully borne out by microscopic examination. My 

 remarks will be chiefly directed to the structure of these two rocks 

 and their relations. 



The matrix of the serpentine is compact, of a dark brownish to 

 greenish black colour, speckled by very minute crystals or granules 

 of a mineral resembling one of the spinellid group. There are 

 irregular patches, two inches or more in greatest diameter, of a 

 greenish-white, steatite-like mineral full of small rounded inclusions 

 of the dark matrix ; so as to form a kind of rude network or cell- 

 like structure. Closely associated with this are crystalline grains of 

 bastite (with the usual rounded inclusions of the matrix), at most 

 about one half of an inch in diameter, and of rather feeble lustre. 

 From the general appearance and relation of these two minerals, one 

 would conclude that the white mineral was the result of a further 

 change of that represented by the bastite. The rock in its general 

 aspect, jointing, fracture, and mode of weathering, corresponds with 

 a true serpentine, such as that of the Lizard. It very closely re- 

 sembles my hand - specimens of bastite - serpentine from Baste 

 (Hartz), Kupferberg (Bavaria), and Sta. Catarina (Elba). Of the 

 first and third 1 possess slides, which prove the rocks to be almost 

 identical. 



The Belhelvie serpentine (rock) consists of the following minerals : 

 (1) Olivine, more or less converted into varieties of the mineral ser- 

 pentine, with separation of the iron in the form of magnetite, etc. 

 I have so often described the gradi;al formation of the " strings " of 

 greenish and rather fibrous serpentine along the cracks of the 

 original olivine, and the way in which they, and sometimes the 

 mineral occupying the interstices between them, are discoloured 

 by the deposit of magnetite, heematite, etc., that it is needless 

 to occupy any space by repeating the usual details. Portions 

 1 It is marked on Dr. A. Geikie's Geol. Map of Scotland. 



