80 REPORT—1874., 
east Black Mountain, Divis, Slemish, and Slieve-na-nee (1782 ft.) ; on the north 
the ground is comparatively low; on the north-west and west, Keady, Donald’s Hill, 
Carntogher (1572 ft.), Craigs-na-shoke (1996 ft. ), and Slieve Gallion Carn (1625 ft.). 
On the south of the lake, forming very low ground, overlying the basalt and extending 
some miles inland, is a thick deposit of plastic clays and sands, with lignite and 
clay-ironstone. 
The basaltic ground terminates on the east and west in high escarpments, from 
underneath which emerge the mesozoic strata, viz. Chalk, Greensand, Lias, and Trias 
(Keuper and Bunter), all of which can be traced on the east from Carrickfergus 
and Belfast, along the valley of the Lagan to Portadown, round by the south of 
the clay deposit, and continuing on the west by Stewartstown, Moneymore, and 
Magherafelt. Underlying these, following the same line, further back, are the 
various members of the Paleozoic strata, Permian, Carboniferous, and Silurian, 
with, on the west, the metamorphic rocks and red granite of Slieve Gallion. 
In this circuit the ground rises more or less rapidly as it recedes, but the general 
dip of the strata, especially the newer, is towards the Lough. 
The principal inflowing rivers are the Upper Bann, Blackwater, Ballinderry 
river, Maal and Mainwater—the outgoing one being the Lower Bann, flowing 
from the north-west of the Lough, through Lough Beg, and falling into the sea 
below Coleraine. 
The most important, as well as most ancient, of these are the Upper Bann and 
Blackwater, draining the country to the south, and passing through what was 
formerly the delta of one or other of them—the great clay-deposit already men- 
tioned. 
These beds have been referred to before by previous writers, Sir Richard Griffith, 
Portlock, and others, but have not been definitely placed with regard to the 
basalt ‘and drift. They lie under a deposit of drift often more than 50 feet thick, 
are very thick, and extend from Ballinderry river on the west, round by Coal- 
island, Roxborough Castle, Portadown, &c., ending at Sandy Bay, co. Antrim, and 
reaching a distance of six miles from the shore at one place. They consist of 
stratified grey and blue clays, sand, and sandstone, occasionally with iron-pyrites, 
irregular beds of lignite, and hard siliceous clay-ironstones. In these reed-like 
oy and well-preserved dicotyledonous leaves are found, and in the clays 
ragments of black wood, apparently pine and oak, but as yet no trace of a fauna, 
They dip towards the lake at from 2°-3°, which would give a thickness of 1200 
feet at the shore. This must be excessive, yet as they were bored (without being 
fully penetrated) to a depth of over 260 feet* (allowing for drift) in Annaghmore, 
more than two miles from the shore, the theoretical depth being 260 feet, it is 
possible that in some places their thickness may be 500 feet. 
The deepest part was therefore originally at the southern end, whereas it is now 
at the northern, and only 105 feet at most. An ice-formed lake would be deepest 
near where the ice first entered. 
The various localities where the clays may be seen (in one place resting on the 
basalt) having been described, the author noticed the plentiful occurrence of round 
pebbles of basalt and chalk flints in them and some beds of lignite; but in no 
imstance was any of the celebrated silicified wood obtained im situ, notwithstanding 
the numerous excavations that have been made for the raising of the clay for 
pottery manufacture. Nor does he consider that the celebrated specimens obtained 
at Sandy Bay by Barton, and referred to by Scouler, Portlock, and others, were 
true silicified wood at all; for they were black, capable of being cut by a spade, and 
only more or less stony, a description that would apply better to pyritous wood. 
The silicified wood is usually found in the drift, not only south, but also north of 
the Lough; and its real locus may, with most probability, be assumed to be the 
basaltic lignite beds. 
The evidence for the order of superposition of the clay-beds was summed up as 
follows :—(1) In at least one instance a similar clay has been observed resting on 
the basalt. (2) That where the two have been found in juxtaposition, the form 
of the ground, not being an escarpment, shows that the soft beds lie uppermost. 
* Griffith, Second Report of Railway Commissioners, p. 22; also Twenty-second Report 
Brit. Assoc. p. 48; and Portlock’s ‘Geological Report,” p. 167. 
