TRANSACTIONS OF THE SECTIONS. 93 
tidal waves and currents, for the continued action of these causes would have de- 
stroyed that distinctive characteristic, viz. the angular shape of the fragments, and 
the pebbles would have been rounded. 
It is evident that we must seek for some other cause; and it seems to the author 
that the agency of ice will alone enable us to arrive at a probable solution of this 
question. 
He is inclined to think that icebergs, as they parted and floated away from the 
glacier, would hardly deposit their burden of moraine matter in the quiet and 
gradual manner in which the materials composing this breccia must have been 
accumulated; besides, none of the fragments show any trace of ice-striz, which 
might naturally have been expected to exist if this had been the means by which 
they were deposited. 
In the seas of the Arctic region, the freezing of the water forms a sheet of ice 
along the shores. When thaw sets in, tons upon tons of rock débris, loosened by 
the frost, tumble down and collect on the ice-foot. The combined effects of heat 
and wind break up this floe-ice into immense sheets, which float away, and melting 
in the open sea, gradually deposit their load over the bed of the ocean. 
Considering this fact in relation to the question now before us, we may be able to 
account not only for the angular fragments, but also for the stratified nature of this 
breccia, as well as the absence of ice-markings on these fragments. Thus the frosts 
of Permian times would freeze the water and waste the pre-existing rocks, and the 
loosened materials would accumulate on similar floe-ice ; these floes, after breaking 
up, would float away and deposit their burden in tranquil water, giving rise to that 
regular bedding which is so characteristic of this breccia. Granting this to con- 
tinue for a sufficient length of time, and we may easily account for the formation of 
a breccia from 90 to 100 feet thick, as in the present instance. 
On the Jointed Prismatic Structure of the Giant’s Causeway. 
By Professor James Toomson, F.R.S.£. 
— On Geological Sections in the co. Down. By Writ1aM A. Trattr, M.A.L., 
ELR.GASTL., of H.M. Geological Survey of Ireland. 
The author exhibited three sheets of geological sections, lately completed by him 
and published by the Geological Survey of Ireland, illustrating the geology of the 
co. Down and a small portion of the'co. Antrim, accompanied by a geological map 
of the entire county on the scale of one inch to the mile (as published), having the 
different lines of sections laid down thereon. The sections themselves were drawn 
to the natural scale, and six inches to the mile. 
Section I. ran from Annalong, about 7 miles south of Newcastle, across the 
Mourne Mountains, Slieve Donard (2796 feet high), to Slieve Croob (1755 feet high), 
thence N.W. by Moira to Derrymore Point on Lough Neagh. 
Section II. from Narrow-water near Warrenpoint, E.N.E., across the Mourne 
Mountains and Slieve Donard to Newcastle. 
Section III. from Soldier’s Point, at the entrance, to Carlingford Lough, N.N.E., 
across the Mourne Mountains to Newcastle. 
Section IV. from Killinchy on the west side of Strangford Lough, N. by Castle 
Espie and Scrabo Hill to near Holywood on Belfast Lough. 
The author gave a brief sketch of the geology of the entire co. Down, with the 
probable order of succession of the different rocks composing it, having representa- 
tives of both the older and the newer formations, and igneous rocks of very different 
es. 
The county for the most part consisted of Lower Silurian rocks, extending from 
the Copelands to Carlingford Lough, being part of the large Silurian tract stretching 
into the south of Scotland, and belonging chiefly to the “Caradoc” or “ Bala ” beds, 
while the Llandeilo beds occur in some places, though a line of demarcation be- 
tween them had not been determined, 
