104. Corr—The Rhyolites of the County of Antrim ; with a Note on Bauxite. 
described, on the other hand, as protruding through the rhyolite, in the form of 
an old volcanic neck; and as such it is represented in a very courageous section.* 
The first statement does not prove anything respecting the relative ages of the 
rocks; but the second, if substantiated, appears convincing. It influenced von 
Lasaulx,t who stated that the rhyolite was, without doubt, the oldest volcanic 
rock, and who quoted the intrusion at Scolboa as decisive. 
Even if the voleanic neck of basalt were an undoubted fact, it might be of 
upper basaltic age; and the rhyolites might still be intrusive in the Lower Basalts. 
In the field, however, I can find no warrant for any definite statement as regards 
Scolboa. The basic rock, on the north side of the farm of Scolboa Upper, is a 
fresh and handsome dolerite, with porphyritic olivine. It overlies the exposures 
of rhyolite, without the junction being exposed; and it has a boldly developed 
columnar structure, even with ‘ tenon-and-mortise”’ details. These columns stand 
vertically, as they readily might do in a lava-flow. Otherwise, the nature of the 
rock might fairly make one regard it as intrusive. Mere inference, however, 
hardly justifies the section which impressed von Lasaulx; and the patch of basalt 
is still, I believe, referred to the ‘‘lower sheets,” ¢.e., to the lava-flows, in the 
issues of the Survey map. On Carnearny, the rhyolitic lava-flows dip under 
the amygdaloidal and fluidal olivine-basalt of the summit; but there is a fair 
interval of moorland between these rocks, and no junction can be traced. 
While Professor Hull,{ who admitted that the ‘‘ actual junction is never seen 
around Tardree Hill,” continued to maintain his view, Mr. G. H. Kinahan § stated 
that the main rhyolite of Tardree was erupted at a later date than some of the 
basalts, and during the progress of general vulcanicity in Co. Antrim. This must 
be regarded as a happy suggestion, borne out by subsequent discoveries at 
Templepatrick. Mr. Kinahan believes, however, that some sporadic eruptions of 
rhyolite occurred prior to the outpouring of the bedded basalts. Sir A. Geikie, || 
in 1888, held the whole mass around Tardree to be intrusive, at any rate in 
the Lower Basalts; but he stated that this view was based solely on analogy 
with the west of Scotland and Templepatrick. ‘The section accompanying his 
paper is put forward as showing ‘‘what is actually seen”; but the junctions of 
the two series are firmly drawn on it, and the rhyolite is given the traditional 
massive character, which is, to my mind, incompatible with its variations in the 
field. The slight references to ‘‘ pitchstone and pearlstone” show, however, that 
the author was prevented from examining the sections at Sandy Braes. 
* Mem. to Sheets 21, 28 and 29 (1876), p. 19. 
} ‘‘ Aus Irland” (1878), pp. 168 and 169. Also op. ect., Tscherm. Mitth., Bd. i. (1878), p. 411. 
{ ‘‘ Phys. Geol. and Geogr. of Ireland,” Ist ed. (1878), p.64; and 2nd ed. (1891), pp. 98 and 99. 
§ ‘‘ Manual of Geol. of Ireland” (1878), p. 162. 
|| Op. ctt., Trans. Roy. Soc., Edin., vol. xxxyv., p. 171. 
