TRANSACTIONS OF THE SECTIONS. 81 
(8) That pebbles of basalt are found in them. (4) That while numerous junc- 
tions of the chalk and basalt are seen, these clays are never found between them. 
(5) The recent aspect of the plant-remains prevents the supposition that the clays 
belong to an older period than the Chalk. The only place left for them is therefore 
between the basalt and the drift, which is seen resting on them. 
Geologists have hitherto differed very seriously as to the age and position of these 
beds. Portlock has classed a portion of them with the Nucula-clays of Derry *, 
which belong to the drift; Griffith with the Bovey Tracey beds; Prof. King above 
these t; Jukes has mapped them as Pleistocene, and Mr. G. H. Kinahan § suggests 
that they are a Preglacial drift: the author proposes to class them as Pliocene, on 
the following grounds :— 
The basaltic outflow was followed by a period of great disturbances and disloca- 
tions, accompanied by very extensive denudations, sufficient to remove in many 
places as much as 1000 or 2000 feet of solid strata. Afterwards the Lough Neagh 
clays were deposited. Thus we have unconformability together with an immense 
> of time, which alone would justify us in placing the basalt (of acknowledged 
locene age) and the clays in different systems. Besides, the plant-remains have 
an exceedingly recent aspect, and the lignite is often not far removed from peat. 
On the whole, the beds bear some resemblance to the Older Pliocene of the Val 
d’ Arno as described by Lyell (‘Student’s Elements of Geology,’ p. 184). The author 
was glad to say that the present classification has met with the sanction of Prof. 
Ramsay and Prof. Hull. These clay-beds must occupy an area of not less than 180 
square miles. 
Around the mouth of the Moyola are clay-beds containing erect tree-stumps, 
forming a small delta of Postglacial date. 
Former level of the Lough.—The clays being found at a height of 120 feet above 
the sea in many places, prove that the waters formerly rose to at least that level, 
whereas they are now but 48 feet above sea-level. They were most probably 
higher, as much of the ancient mud must have been denuded away since its 
deposition; but if the shore be contoured at even 120 feet, the former area of the 
lake must have been nearly double what it is now, or nearly 800 square miles. 
The author considered the evidence to prove that the lake extended southward 
towards Armagh, and but little more to the north than it now does, the deepest 
part lying also to the south. 
Time and Mode of Formation.—It is clear, therefore, that the lake was formed at 
the close of the Miocene period (the Pliocene clays denoting the time of its 
completion), and it is therefore unlikely that ice could have had any thing to do 
with it, the slight trace of ice-action elsewhere during that time being most 
probably due to a local glacier; but to produce any thing like the effects here to be 
seen, such as the removal of thousands of feet of rock over hundreds of square miles, 
would have necessitated a very intense degree of glaciation, and such as must have 
left distinct traces behind it. Mr. J. F. Campbell, F.G.S.||, has indeed attributed 
the shaping of this district to the ice of the last Glacial epoch. But this opinion is 
hardly tenable; for the lake, and consequently the general physical geography of 
the district, was formed previous to that time. 
The author’s theory of the formation of the lake is this:—After the basaltic flow 
had ceased, subsidences over a large area took place, corresponding with certain 
lines of parallel and transyerse faults of considerable force, which can be proved to 
extend across the ground comprising the plain and bed of Lough Neagh. Their 
general effect would be to give to the face of the country a rudely depressed shape, 
consisting of a series of steps to the north, north-west, and south, thus determining 
the chief flow of water into the hollow centre, and. (denudation proceeding pare 
passu) gradually shaping out something like a lake-basin. The egress of the water 
was provided towards the east, along what is now the valley of the Lagan, which, 
* Portlock’s ‘Geological Report.’ 
t Report to accompany Geological Map, 1838; also Report British Association, 1852, 
. 48. 1 3 
t Synoptical Table of Rock Groups. 
§ Geological Magazine, vol. i. p. 173. 
|| Quart. Journ. Geol. Soc. London, May 1873. 
