146 Professor G. C. Gough 
Metamorphism of Chalk. 
altered chalk at Scawt Hull, an old volcanic neck, about 6 miles 
north of Larne, came upon a dyke traversing the ‘neck’ dolerite of 
the hill and cutting across a narrow band of chalk. The geological 
structure of the district is that common to the basaltic plateau of 
Antrim, and consists of the basic lava-flows covering the Chalk and 
other Mesozoic beds, the chalk being the usual hard variety of 
Ireland. Of this hill the Irish Survey Memoir to Sheet 20 states 
that ‘‘at Sheve Scawt the Chalk has been carried up with the basaltic 
mass forming ‘the volcanic neck. By igneous action it has been 
converted into a highly crystalline saccharoidal marble.”” Miss Andrews 
informs me that ‘‘the band of chalk appears to project horizontally 
into the ‘neck’; and the dyke, which is between 8 and 4 feet wide, 
is running vertically through the ‘neck’ cutting across the tongue of 
chalk.” The chalk had weathered so much that it was quite 
unexpectedly that she came upon the dyke. Miss Andrews obtained 
various samples from different points, and after having sections cut 
kindly handed them over to me. The specimens include (i) the rock 
forming the ‘neck’ and which she thinks has carried up the chalk; 
(ii) the dyke which runs through the neck; and (iii) the chalk in 
various stages of metamorphism. 
Number I, may be dismissed very briefly, as it is one of the typical 
igneous rocks of the district, namely, a fine-grained ophitic dolerite. 
It is holoecrystalline, the minerals being augite, felspar, olivine, and 
magnetite. The augite is in rather large pale-brown non-pleochroic 
crystals, broken up by longish Jath-shaped crystals of plagioclase 
which appear to be labradorite. The olivine is roughly idiomorphic, 
generally clear and colourless, but changed to yellow serpentine along 
the cracks. 
Number II (Pl. V, Fig. 1), the dyke, proves to be a very interesting 
rock. It isa granitoid, holocrystalline, basic rock, and may perhaps 
be best classed with Harker’s ‘‘ diabases without olivine,’’ although its. 
granitoid structure would almost lead one to call it a gabbro. Its 
most striking feature is its beautifully pleochroic augite, which is 
found in well-marked eight-sided crystals. These augites are apparently 
titaniferous, with a pleochroism varying from a dark lilac to yellowish 
green and frequently showing the hour-glass structure. They are 
well-zoned, and in some cases show undulating extinction, but in the 
majority of crystals, although there is a well-marked outer zone 
suggesting a different composition, it extinguishes at practically the 
same angle as the main mass of the crystal. The felspar has 
decomposed, and is filled with feathery, and radiating decomposition 
products, so that it is not possible to distinguish the variety. No 
olivine was detected, but a little interstitial quartz was found, while 
apatite in small but well-marked prisms is fairly frequent. Iron-ores 
are also plentiful, the chief being magnetite, in places having a kind 
of reaction rim of actinolite(?); ilmenite is present, as is also pyrite. 
The first noteworthy change in the chalk is seen in a section from 
20 yards away from dyke. Here the organisms have disappeared, and 
the chalk has become finely granular owing to the development of fine 
crystals or grains of calcite. About two yards from dyke the chalk 
has become a typical crystalline limestone with large crystals of 
