Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/266

164 value of this ore. The poorer kind, as lithomarge, may he used as a flux, while the richer bole and pisolite are made to yield a superior iron, suitable alike for steel- or machinery-purposes*.

The growing demand for this Antrim ore proves its utility; during the past year upwards of 50,000 tons were shipped to England from several ports along the Antrim coast. The mining has become a steady and increasing industry in the county.

VI. General Conclusions.

1. That during the period of volcanic activity in the N.E. of Ireland, there was a cessation of igneous eruption over certain areas, during which lacustrine deposits were formed, and a growth of terrestrial plants took place.

As to the extent of the lake, or of the land-surface, the data are incomplete to form any conclusions. The lignite in the Giant's- Causeway basalt, the leaf-beds of the Isle of Mull, and the bituminous deposits in other localities may be on the same horizon. However, it is perhaps more probable that these several land-accumulations may have been formed in isolated areas, though during the one period of rest in the volcanic forces.

2. The preceding remarks imply that there were at least two periods of volcanic activity, the plant-beds or lignite marking an unconformability of an upper basaltic series to a lower. The plants being of Upper-Miocene age enables us to assign a position in the scale of geological time to the superior basalts. What may be the age of the inferior series, is a question that can only be approximately answered. That it is newer than the White Limestone (Upper Chalk) and older than the upper Miocene, is apparent.

3. The older basaltic series has undergone metamorphic changes in the composition of some of its interstratified lavas. The boles and ochres, which are decomposed basalts, are probably connected with subaqueous igneous flows, whilst the pisolitic iron-ore band, which is a metamorphosed bole, indicates subaerial action, and that during the period of emergence the bole was subjected to further metamorphism by heated superimposed basalt.

Discussion.

Mr. D. Forbes was not prepared to admit some of the theoretical conclusions of the authors, and objected to calling in metamorphism to account for all that was hard to be understood. He could not recognize the division of beds so similar in character into two classes. He wished to know, assuming that the iron-ore merely resulted from the decomposition of the basalt, what became of all the silica and alumina which constituted three-fourths of the mass. The origin of the pisolitic ores was in fact organic. In Sweden certain lakes were regularly dredged each year for the pisolitic ore still in

the ore could be smelted at home. Furnaces might easily be erected near the mines for the reduction of the richer pisolite ; limestone is abundant ; and coal can be procured easily and cheaply from Scotland.
 * It would be of great importance to the prosperity of the north of Ireland if