Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/264

162 3. Origin of the Ore. — The mode of occurrence of the conglomerate bed of iron-ore and the associated strata clearly demonstrates a sedimentary origin. The lignite has been derived from a plant-growth in situ, upon an eroded surface of basalt. The shaly beds have originated in the tranquil deposition of argillaceous and arenaceous materials mingled with some ferruginous matter, all derived from the degradation of basaltic rocks in the immediate vicinity. The presence of fragments of plants, chiefly leaves and small branches (for rarely do we find large pieces of wood), points to the growth of a terrestrial vegetation near the margins of a morass, or sheet of water, probably a lake. The finely laminated structure of the strata and the delicate nature of the parts of the plants preserved require a tranquil accumulation by aqueous agency.

The conglomerate-bed results from the degradation of the pisolitic iron-ore, of which it is chiefly reconstructed, and of the underlying ochres : it appears to have rapidly formed, and, so far as we know at present, brought to a close that period of rest in the volcanic activity during which these sedimentary beds had been accumulating.

The following analyses of the more spheroidal portion of the Ballypalidy ore indicate a close affinity with the pisolitic iron-ore of Tully, near Glenarm (see p. 159), and confirm our observations as to the source whence the ferruginous materials of the irregularly stratified beds at Ballypalidy have been derived.

Analyses of Brown Aluminous Haematite *.

Sesquioxide of iron 35.91 27.93

Protoxide of iron 6.57 5.08

,, of manganese 0.05 tr.

Alumina 27.95 34.57

Lime 0.60 0.91

Magnesia 0.20 0.62

Potash 0.49 —

Silica 9.75 9.87

Phosphoric acid — tr.

Water 18.60 19.36

Titanic acid — 3.51

100.12 101.85

4. Plant-remains of the Series. — Though Mr. Baily's account of the plants found at Ballapalidy is the first published record of the occurrence of vegetable remains associated with the basalts of Antrim, yet their presence in these same beds was known as early as 1862, soon after the commencement of mining operations at that locality. The discovery we owe to Mr. Rowland Smeeth, a pupil of one of us ; and it was made public in a course of geological lectures delivered at Belfast. The plants then obtained were few in number, Pinus and Cupressites being the only forms identified. But the priority of discovery of plants in the Antrim basalt we accord to Dr. J. Bryce, F.G.S., who, with an unaccountable diffidence, hesitated to make known his researches, though a favourable opportunity offered on the


 * Percy, Metallurgy of Iron, p. 207.