VII.—On the Age of the Trachytic Rocks of Antrim

Extract

Since the publication of the Geological Survey Maps and Memoirs of Antrim, some additional evidence has been obtained bearing on the age of the trachyte of that district. In the year 1888, when engaged in traversing a line of section running from Belfast in a northerly direction across county Antrim to the Giant's Causeway, I was fortunate enough to notice in a large chalk quarry at Templepatrick railway station evidence which seemed to show that the trachyte was later than the Tertiary basalt sheets of the lower division; and, on further investigation into this interesting subject, additional evidence was procured that the trachytic eruption was older than the sheets of the upper series, and was, so to speak, of mid-basaltic age. Subsequently I accompanied the Director-General, Sir Archibald Geikie, on his visit of inspection to this locality, and he approved of my views. Professor Gilbert, of the United States Geological Survey, who was with us at the time, also agreed with the conclusions arrived at.