70 REPORT—1874. 
the vents of eruption are now visible, either in the form of amorphous masses of 
trap protruded through the sheets, or of great funnels filled by bombs, broken 
pieces of rock, and ashes, such as the rock on which is perched the venerable ruin 
of Dunluce Castle (the ancient stronghold of the MacDonnells), or the neck erupted 
through the Chalk in the coast-cliffs near Portrush*. One of these old funnels 
was found by the late Mr. Du Noyer near this place: it forms a portion of the 
crest of the ridge overlooking Belfast Lough, to the east of Cave Hill, and is 
within easy reach of Members of the Association. 
The period of the formation of the older sheets appears to have been brought to 
a close by the discharge of volcanic ashes and the formation of an extensive lake, 
or series of lakes, over the region extending at least from the shores of Belfast 
Lough to the northern coast of Antrim, in which the remarkable beds of pisolitic 
iron-ore were ultimately deposited. This is the only mode of origin of these ores 
which seems to me at all probable; and I am consequently unable to accept the 
views advanced by Messrs. Tate and Holden regarding their origin from basaltic 
lava by a process of metamorphism. That water was present, and that the beds of 
ash which underlie the pisolitic ore were stratified, at least in some instances, is 
abundantly evident upon an examination of the sections at Ballypalidy, Ballymena, 
and the northern coast. In some places they are seen to be perfectly laminated in 
a manner that could only take place by the agency of watert. It would seem, 
therefore, that by the combination of slight terrestrial movements a shallow basin 
was formed over the area indicated, which received the streams charged with iron in 
solution, draining the upland margins, from the waters of which were precipitated 
the iron, possibly by the agency of confervoid aleve, as in the case of the Swedish 
lakes of the present day (a view maintained by Mr. D. Forbes, F.R.S.), or by the 
escape of carbonic acid, owing to which the iron became oxidized and was pre- 
cipitated. 
Upon these uplands grew the plants whose remains occur amongst the ash-beds 
of Ballypalidy, the Causeway, and elsewhere, and which have enabled Mr. Baily 
to refer the strata in which they occur to the Miocene period}. In some places 
the vegetation crept over the surface of the former lake-bottom as it became 
shallower or was drying up, and gave rise to beds of lignite similar to those 
described by the Duke of Argyll as occurring at intervals amongst the basalts of 
Mull§. The beds of ore, wherever they are found, belong to one and the same 
geological horizon, and enable us to separate the basaltic series into two great 
divisions—one below, and the other above the position of the pisolitic ore; and 
which, on maps of the Geological Survey, will for the future be represented 
by two different shades of colouring. 
The ore itself is now laid open in numerous adits driven into the hill-sides, or in 
open works at Island Magee, Shane’s Hill, Broughshane, Red Bay, Portfad, and 
other places||, whence it is transported to the furnaces of Scotland, Cumber- 
land, Lancashire, and Wales. A new source of industry and wealth is rapidly 
springing up over the already prosperous county of Antrim, and ere many years 
are over we may expect to see furnaces established at several points for smelting 
the ores at the mines from which they are extracted. 
The period of volcanic inaction just described was brought to a close by fresh 
eruptions of augitic lavas, which spread in massive sheets over the beds of ore, 
bole, and even lignite, without materially altering their constitution. Thus on the 
* A sketch of this old rock is given by Professor Geikie in Jukes’s ‘Manual of Geology,’ 
ord edit. p. 271. : i 
+ The authors referred to, while admitting the stratified character of the beds at 
Ballypalidy and their formation in presence of water, consider that in all other cases the’ 
iron-ore has been formed on a terrestrial suriace; but sections seen at Ballymena and 
the north coast have led me to conclude that these beds are all more or less stratified, and 
due to aqueous deposition. 
t Quart. Journ. Geol. Soe. vol. xxv. p. 357, pls. 14 & 15. The plants determined by 
Mr. Baily, from Ballypalidy, belong to the genera Sequoia, Cupressites, Rhamnus, Quercus, 
Pinus, ke. They were originally detected by the late Mr. Du Noyer. 
§ Jukes’s ‘ Manual of Geology,’ 3rd edit. p. 690. 
|| At Pleaskin Head it was originally observed by the Rey. Dr. Hamilton (1790). 
