248 Br. J. A. Smytlie — Inclusions in 



in great part of felspar, the crystallization of which in contact with 

 the films is evidently the cause of the surface structures of their 

 facets, while but little felspar usually separates the films from the 

 surrounding whin, so that actual contact is at times inevitable. 



The thickness of the crystalline coating of both knobs and moulds 

 is verj'' slight; in fact, the crystallization-phenomena seem to be 

 merely a surface-effect. Scrapings of the coatings appear, by 

 examination in polarized light, to consist of the same felspathic 

 material which is the prime constituent of the inclusions. 



The films, which part the knob-surfaces and the moulds, have 

 a bronze-yellow, rarely pyritic coloration,, becoming olive-green in 

 certain lights. They can be easily scaled off either knob or mould ; 

 their thickness is about that of ordinary writing-paper ; they are 

 opaque, sink in Sonstadt solution of specific gravity 3-1, are strongly 

 attracted by a bar magnet, and, in fact, show marked polarity. 



Both surfaces of the films show crystalline structure, though 

 without correspondence in grouping and orientation, and a similar 

 lack of correspondence exists between the structure of the film-surfaces 

 and those of knob or mould in contact with them. The crystalline 

 markings differ somewhat from those described above, taking the form 

 rather of narrow ridges or troughs, grouped in parallel lines or tufty 

 aggregates, sometimes on either side of an axis (PI. XVII, Fig. 5). 



Minute plates of reflecting mineral found, not infrequently, within 

 inclusions usually exhibit the same structures as the films. 



When fragments of the films are digested in warm, fairly con- 

 centrated hydrocliloric acid they quickly dissolve. The residual powder 

 is non-magnetic, the solution contains ferrous iron and titanium, and 

 the gases evolved respond readily to the tests for hydrogen sulphide. 

 These observations were confirmed on a complete small inclusion; 

 after short immersion in the acid the film was dissolved, disclosing 

 the knob-facets, characteristically marked. Microscopic examination 

 of the films shows them to be sometimes composite, but the above 

 reactions prove that the bronze-coloured mineral is pyrrhotite. It is 

 difficult to say whether the magnetic ju-operties of the films are due 

 only to this mineral or partly to admixture with magnetite, but it 

 is significant that the films in one specimen, which had a pronounced 

 pyritic colour, were devoid of magnetic properties. 



The Petrology of the Inclusions. 



Thin sections show very considerable differences between the 

 inclusions and the surrounding whin. The latter is noi'mal in 

 character, and the inclusions differ from it, broadly speaking, in being 

 much finer in grain, in the comparative absence of augite, and the 

 presence of a large amount of felspathic material and some quartz. 



Of the mineral constituents, felspar greatly predominates, and 

 oxides of iron appear more plentiful, as a rule, than in the normal 

 whin, despite tiie smaller yield on analysis. This is to be explained 

 by the rarity of augite, nearly all the iron being visible in the form 

 of opaque minerals. 



The felspar exists in two forms ; in groups of well-crystallized 

 individuals, like those in the normal whin, though at times with the 



