208 Prof. Hull — The Volcanic History of Ireland. 



cutting of Ballypallidy,' by tlie late Mr. Du Noyer. The identity of 

 these plants with those of Miocene age establishes the geological age 

 of the basaltic lavas on which they repose, as also their coincidence 

 in time with the basalts of Mull and the Inner Hebrides, first de- 

 termined by the Duke of Argyle, with the assistance of the late 

 Prof. E. Forbes. 



At the close of this period of repose a new outburst of volcanic 

 activity took place, and great sheets of augitic lavas were poured 

 over the older beds, to a depth of 400 or 500 feet in some places. 

 Amongst the old necks or vents belonging to this thii'd period, pro- 

 bably those of Dunluce, filled with large bombs, and of Sleamish, 

 an abrupt isolated mass of basalt rising above the surrounding 

 country, may be identified ; but the craters have entirely dis- 

 appeared, and we can only recognize occasional] }'■ the truncated 

 throats by which they communicated with the interior of the earth's 

 crust. 



The third period of volcanic activity seems to have been ac- 

 companied or followed by the production of immense numbers of 

 nearly vertical dykes — filled with basalt — which traverse not only 

 the older sheets, but the newer. The production of these dykes 

 seems to have been the result of the final effort of the elastic gases 

 and steam which are the motive forces in volcanic eruptions. In 

 order to account for the existence of these dykes — which would 

 occupy a considerable area if placed side by side — it is necessary 

 to suppose a general inflation or bulging of the earth's crust in this 

 region. Such an inflation would be accompanied by the formation 

 of fissures, which, when filled in with molten lava from below, 

 would, as it seems to me, result in the production of the dykes to 

 which I have referred. 



The whole of the volcanic operations here briefly described appear 

 to have been subaerial. If submarine — as has often been supposed — 

 we might expect to have found marine strata accomj)anying some 

 of the beds of lava ; but these are altogether absent, and the various 

 bands of red bole can be regarded as nothing else than lava, or 

 volcanic ash decomposed in presence of the atmosphere. The 

 microscopic structure of some of the more compact beds of bole 

 bears out this view. 



It is very remarkable, considering the comparatively modern 

 period of these volcanic phenomena, that, as far as we know, none 

 of the original craters are to be found over the whole region. Here 

 and there, indeed, we find the pipes or throats of the old volcanos, 

 but the original craters have been obliterated. On the other hand, 

 if we cross over to Central France, we find in the region of Mont 

 Dore ancient craters in a remarkable state of preservation, and 

 which were, apjoarently, contemporaneous with those of the north 

 of Ireland. To the same period are also referable (in all probability) 

 some of the volcanic cones of Germany, Hungary, Transylvania; 

 and it is unquestionable that the Miocene period was one of extra- 

 ordinary volcanic activity over large European areas, in which the 

 1 Quart. Journ. Geol. Soc. Lond. vol. xiv. p. 357 (with plates). 



