CHAP. XLI 
VENTS OF THE BASALT-PLATEAUX 
273 
rock is an ophitic dolerite consisting of plagioclase, augite, and iron oies, 
without olivine, enclosing one or two patches of finer basalt. The vesicles 
in the latter, and certain angular spaces between the crystals of the former, 
have been wholly or partially filled with brown glass, the outer part of which 
has been converted into radiating crystals of a brown mineral.” The 
occurrence of patches of 
glass which seem to have 
O 
been squeezed into vesicles 
or cracks in the body of a 
dolerite or andesite has been 
noticed in some of the 
Tertiary dykes. But in 
the present case the glass 
occurs as a mere coating on 
the walls of the larger 
spheroidal vesicles, the in- 
terior of which generally 
remains empty. 
Of the other doleritic 
necks scattered over the 
surface of the Antrim plateau, I will refer to only one which occurs on 
the hill-slopes between Glenarm and Larne. It forms a prominence known 
as the Scawt Hill, and consists of a boss of basalt, which, in rising 
through a vent in the plateau-sheets, has carried up with it and converted 
into marble a large mass of chalk which is now exposed along its eastern 
wall (Fig. 296). , 
As examples of similar necks which have been exposed by denudation 
outside the present limits of the same plateau, I may allude to those which 
rise through the Cretaceous and other Secondary strata on the northern 
Fig. 296. — Section of the east side of Scawt Hill, near Glenarm. 
a, "bedded basalt ; b, mass of chalk ; c, basalt neck. 
a a, Chalk ; b, neck. 
coast near Ballintoy. One of the most striking of these may be seen at 
Bendoo, where a plug of basalt, measuring about 1400 feet in one diameter 
and 800 feet in another, rises through the Chalk, and alters it around the 
line of contact (Fig. 297). Another remarkably picturesque example is to 
be seen near Cusliendall, where a prominent doleritic cone rises out of the 
VOL. II 1 
