Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/510

 closed in the Wealden, and that its fossils have an Upper Neocomian character, with a clear affinity to a Spanish series. He regarded the Wealden of North Germany as not strictly contemporaneous with that of England, and stated that the " Hilsconglomerat " in Brunswick was a shore-deposit, hut that its relation to the Wealden could not be observed.

2. On Deep-mining with Relation to the Physical Structure and Mineral-bearing Strata of the South-west of Ireland. By Samuel Hyde, Esq.

(Communicated by E. Etheridge, Esq., F.G.S.)

[Abstract.]

The author described the general structure of the country in the south-west extremity of Ireland, which he stated to consist of a series of rocks analogous to the " Killas " of Cornwall, and belonging to the upper part of the Lower, or the lower part of the Upper Devonian series. He combated the opinion which had been expressed by the late Professor Jukes, that copper-ores would not be found in the district in sufficient quantities to make mining there a remunerative process. In support of his thesis, he cited the Bearhaven mines, established about fifty years ago, the Allitries and Ballycummisk mines, and the Coosheen mine. He stated that in the Ballycummisk mines a depth of 200 fathoms has been reached, and that some of the shafts at Bearhaven are much deeper. These deep workings were said to yield large returns of ore. In opposition to the opinions stated by the late Professor Jukes, the author maintained that the copper lodes were of the same nature as those of Cornwall, and he described them as running in a similar direction, namely, 10°-25° N. of E. From the similarity in the geological constitution of the country, and in the direction of its mineral veins, the author was inclined to infer a former continuity between the south-western promontories of the islands of Great Britain and Ireland.

Discussion.

Mr. David Forbes protested against the notion that the Devonian strata themselves were metalliferous, the veins being of much later date — in the present case Postcarboniferous. He maintained that there was no valid reason for supposing that the veins became unproductive with increased depth, and opposed the notion that they had been filled in by segregation from the surrounding rock. He alluded to the use of spectroscopic analysis in such inquiries, and remarked that as no trace of copper is to be found in the rock even immediately adjacent to veins, we should have to admit, on the hypothesis of segregation, that the rock must originally have contained precisely the amount of metal segregated in the veins.

Mr. Etheridge agreed with Mr. Forbes as to the date of the filling in of the veins. He also maintained the justice of correlating the rocks with those of the Cornish area.

Mr. Hyde briefly replied.