272 
THE TERTIARY VOLCANOES 
book vi i r 
able, the basalts appear somewhat indurated, break with a peculiar splintery 
fracture, and weather with a white crust. These characters are still better 
shown on abundant fragments which may be picked up among the debris 
further up the slope. There can be no doubt, I think, that a ring of flinty 
basalt, differing considerably in texture from the usual aspect of that rock 
in the district, surrounds the neck. The meaning of this ring will be more 
clearly seen from the description of another example in Mull. About four 
Flu. 294. — Slemish, a Volcanic Neck or Vent 011 tlie Antrim Plateau, seen from the north. 
miles to the north-east of Slemish, a smaller and less conspicuous neck rises 
out of the plateau-basalts. The rock of which it consists is less coarsely 
crystalline than that of Slemish, but its relations to the surrounding vol- 
canic rocks are obviously the same. On the west side of Belfast Lough a 
boss of similar rock, about 1200 feet in diameter, rises at the very edge 
of the basalt escarpment into the eminence known as Carnmony Hill (Fig. 
295). On its northern side it presents along its wall a mass of interposed 
volcanic agglomerate. 1 On visiting with Mr. M'Henry the quarry opened 
on the. eastern face of this vent, I was much struck with the remarkable 
Fig. 295. — Section of Volcanic. Vent at Carnmony Hill (E. Hull). 
T, Lower basalt ; C, Cretaceous strata ; L, Lower Lias ; M, Triassic marls ; V, Vent. 
cellular structure of some parts of the dolerite. Many of the vesicles are 
lined with a thin pellicle of black glass, and the same substance occurs in 
minute patches in the body of the rock. A thin slice exhibiting this 
structure was found by Mr. Watts to possess the following characters : — ■“ The 
1 This neck was recognised by Du Noyer in 1868 as “one of the great pipes or feeders of the 
basaltic flows.” See Prof. Hull, Explanation of Sheets 21, 28 and 29, Geol. Survey of Ireland 
(1876), p. SO. 
