428 
THE TERTIARY VOLCANOES 
BOOK VIII 
Hebrides, and hence the stratigraphieal relations of the two groups are apt 
to be misunderstood. What is actually seen is represented in Fig. 371. 
The lithoidal rhyolite emerges from underneath the basalts which abut against 
its sloping surface, forming on the north side of Carnearny Hill a steep bank 
about 150 feet above the more gently inclined slope below. The basalts 
consist of successive nearly level sheets of compact and amygdaloidal rock. 
It is obvious that only two explanations of this section are possible. 
Either the rhyolite was in existence before the basalts which flowed round 
it and gradually covered it, or it has been erupted through these rocks, and 
is therefore of later date. 
The former supposition has been the more usually received. The 
rhyolite has been supposed to form the summit of an ancient volcanic dome, 
perhaps of Eocene age, which had been worn down before the outflow 
of the plateau-basalts under which it was eventually entombed. Had this 
been the true history of the locality, it is inconceivable that of a rock which 
decays so rapidly as this rhyolite, and strews its slopes with such abundance 
of detritus, not a single fragment should occur between the successive beds 
of basalt which are supposed to have surrounded and buried it. Though the 
several beds of basalt are well exposed all round, 1 could not, on my first 
visit, find a trace of any rhyolitic fragments between them, nor had Mr. 
Symes, who mapped the ground in detail for the Geological Survey, been 
more successful. I have since made a second search with Mr. M'Henry, but 
without detecting a single pebble of the acid rock among the basalts. Yet 
it is clear from the upper surfaces of some of these lavas that a considerable 
interval of time separated their successive outflows, so that there was oppor- 
tunity enough for the scattering of rhyolite-debris had any hill of that rock 
existed in the vicinity. 
Again, little more than a mile to the east of Carnearny Hill, an outlier 
of the basalts forming the prominent height of the Brown Hod lies upon and 
is completely surrounded by the rhyolite, which along the east side of the 
hill can be traced as it passes under the level sheets of basalt. The line of 
junction ascends and descends on that flank of the outlier, so that successive 
flows of basalt are truncated by the acid rock. But I could find no rhyolitic 
debris between them. 
It appears to me, therefore, that the relations between the two groups of 
rock in this area are similar to those between the granophyres and bedded 
basalts on the south side of Loch na Keal in Mull (p. 396). In other 
words, the rhyolites have risen through the basalts, and are therefore younger 
than these lavas. This conclusion is corroborated by the actual proofs of 
the intrusion of rhyolite into the basalts at Templepatrick. 
All the known rhyolitic masses in Antrim are confined to the Lower 
group of basalts. 1 And as they traverse some of its highest members, 
1 The only exception to this rule was believed to be that of the mass at Eslerstown, four 
miles east of Ballymena, which, as originally mapped, was shown as crossing from the Lower 
into the Upper basalts. Mr. MtHenry, however, has recently ascertained that the acid rock is 
entirely restricted to the area of the older group. 
