446 D. Balsillie— 



felspar. The accessory minerals include chestnut brown biotite, 

 in ragged scales and plates, iron ores, analcite, apatite, and magnetite: 

 there are also clumps of strongly birefringent zeolites. 



Many sections of the rock are remarkably fresh, with the olivine 

 traversed by only a few serpentinous cracks or enclosed in a film 

 or sheath of serpentine. The best specimens are to be obtained 

 from the escarpment or crag in the fields to the south of the quarry 

 that has been opened in the north-western portion of the sill. As 

 mapped, the intrusion extends east towards the Peat Inn-Baldinnie 

 road, but the rock there exposed is a pyritiferous quartz-dolerite, 

 and probably does not belong to the same mass. 



The above rock may be regarded as a typical ophitic olivine- 

 dolerite, and is of a kind that is not common in East Fife ; indeed, 

 the only other mass showing sim.ilar characters is that which occurs 

 at Wilkieston, 5 miles to the south-west of St. Andrew's, which has 

 been described in the Memoir. But here the rock is much less fresh, 

 and shows a curious hypersthene-like weathering of its olivine. 

 Also there is a large quantity of transfused chloritic matter. 



(2) Kilhrachnont and Baldutho type. — Olivine-dolerites, of which 

 the masses exposed at these localities may be taken as the 

 type, are abundant in East Fife. The structure is not ophitic, as 

 in the rock of Gathercauld, but in respect of their olivine content 

 inclined to be porphyritic : that is to say, larger crystals of olivine 

 lie in an environment of felspar laths and pyroxenes ; the latter 

 tending to occur as small idiomorphic prisms rather than as large 

 plates. The rocks of Kilbrackmont and Baldutho are often 

 beautifully fresh in section, and show large olivines, frequently 

 with a marshalling of little idiomorphic pyroxenes round their 

 margins ; the avenues between adjacent crystals being somewhat 

 more highly felspathic. Biotite, iron ores, apatite, and interstitial 

 analcite occur as accessories. 



The intrusions of the Denhead, Mount Melville, Gilston, Balcarres, 

 and Kinaldy districts all belong generally to the above type of 

 dolerite, though there are, of course, great variations in detail, and 

 especially is that remark applicable to the matter of texture. Some- 

 times a flow or pseudo-flow structure may be observed, as in the 

 small intrusion at Blindwells, near Largo. An especially fresh 

 and interesting rock is that of Dunicher Law, east from the Backmuir 

 of New Gilston. Here there is a high content of olivine and a 

 tendency for the pyoxenes to segregate. Th e felspar is finely twinned 

 on the albite and Carlsbad laws, and it is easy to make out that 

 there is a range of plagioclase extending from labradorite through 

 andesine to oligoclase, the first mentioned, of course, greatly pre- 

 dominating. Biotite occurs in small amount, and there is a little 

 interstitial analcite. The Dunicher Law rock is interesting as 

 affording a passage to the Kingask intrusion, mentioned below. 



The masses of Mount Melville, Denork, and Drunicarrow may 

 be described as coarser varieties of porphyritic olivine-dolerite. 



