Note 74 — Chapter XXX · THE CARBONIFEROUS VOLCANOES OF IRELAND

Explanation of Sheet 144, p. 27.

[75] Some of them, however, have characters that rather seem to place them with the intrusive materials of the district, and therefore not necessarily earlier than the bedded lavas and tuffs. The boundary line of the volcanic series is not consistently followed along the same horizon on the Survey maps. Thus to the east of Caherconlish, a strip of the Upper Limestone is inserted below the base of the tuffs for a distance of about four miles. Unless a different horizon has been in some places taken for the boundary between the two groups of limestones, it would appear that the eruptions had not extended over the north and north-east of the district until some time after the deposition of the Upper Limestone had begun. The division between the two limestone groups is taken at a set of chert-bands, but as these are not constant it is sometimes difficult to draw a satisfactory line of division.