776 T. G. B0NNEY ON THE SEBPENTINB AND 



refracting serpentine, and the distinction between " string " and non^ 

 doubly refracting " mesh " is less conspicuous. Much of the iron is 

 disseminated in extremely minute granules over the field, which, with 

 crossed Nicols, shows us fibrous serpentine extending towards the 

 centre of the mesh and sometimes occupying the whole. Where 

 these strings are most clearly defined they exhibit a rough paral- 

 lelism, and the fibrous structure is at right angles to them. The 

 serpentine is irregularly banded with chrysotile. One vein shows 

 unusually bright colours with crossed Mcols. There are two or 

 three grains of a rich brown mineral, probably picotite. Here and 

 there is a little of a fibrous, very strongly dichroic, green mineral, 

 changing from light green to almost black. Altered bronzite is 

 present in rather small grains, and a clear yellowish mineral with 

 very minute belonites, about -001 inch in length, crossing nearly at 

 right angles, so as to form a sort of prismatic reticulation. A similar 

 mineral is abundant in a serpentine from Menheniot (Cornwall), and 

 in one from Santa Catarina, Elba, both of which rocks have some 

 resemblance to this (though containing felspar). I am disposed, 

 after examination of the latter and of bastite rock from the Hartz, 

 to think this mineral either bastite or closely related to it*. 



To the south of Carleton Eoot we find serpentine of a red colour. 

 This also thrusts itself into great masses of the "dioritic" series, 

 which here is also often of a dull red colour. Bronzite crystals, and 

 many thin irregular veins of chrysotile, occur in the serpentine, 

 with occasionally rudely parallel layers and grey veins of a more 

 decomposed serpentine. A great block on the shore, near the road- 

 cutting, just south of the headland forming Carleton Port, shows an 

 intrusive mass of serpentine and several small patches of the same 

 adhering to the side. The block is finely and sharply jointed, and 

 its surface has a glazed aspect. It is a dark-coloured rock, resem- 

 bling a basalt. Red serpentine now becomes more frequent than 

 the dark-green variety. The whole mass has a rather disturbed 

 appearance : in one place there is a little serpentine breccia, pro- 

 bably a friction-breccia ; in another place there are some curious 

 dark veins in the red serpentine. 



By the stone marking five miles from Ballantrae a compact dark 

 serpentine again occurs, with roughly parallel steatitic bands, some- 

 times from 2 to 3 feet thick, and occasionally a greenish serpentine 

 mottled with white steatite. Beyond this we come, a little to the 

 south of Burnfoot, to a compact mottled dull-red variety of serpen- 

 tine, with very small bronzitic crystals, beyond which we reach to 

 the cliffs of porphyrite about Balcreuchan Port. These rocks, however 

 (with a small intrusion of serpentine), will be noticed in due course. 



The following is a description of the microscopic character of two 

 varieties of the red serpentine from the above district : — ■ 



(1) Specimen from south of Burnfoot. In general structure this 

 resembles the other, except that the "meshes" are often partly or 



* Boricky (Basaltgest. Bohm. pi. 1) figures a rather similar arrangement of 

 belonites in a magma basalt, and observes that they resemble the skeleton of 

 an augite crystal, 



