128 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Par to the west, in the Golden Yale of Limerick, yet another group 

 of puys may be found, which rose from the floor of the Carboniferous 

 Limestone sea, and threw out showers of ashes and streams of lava. 

 These, the most westerly remains of Carboniferous volcanoes within 

 our borders, are the only examples which, so far as I know, occur in 

 Ireland. Though the Carboniferous formations are so widely spread 

 over the island, and exposed in so many natural and artificial 

 sections, they have nowhere else yielded evidence of interstratified 

 volcanic rocks. ^ The Limerick puys seem to have risen as a solitary 

 group several hundred miles from their nearest contemporaries. 



The total area within which the puy-eruptions of Carboniferous 

 time took place was thus considerably less than that over which the 

 volcanoes of the Lower Old Red Sandstone were distributed, yet its 

 vents were scattered across the larger part of the site of the British 

 Isles. Prom the vents of Pife to those of Limerick is a distance of 

 above 300 miles ; from the latter eastward to those of Devonshire is 

 an interval of 250 miles ; while the space between the Devonshire 

 volcanoes and those of Pife is about 400 miles. In this triangular 

 space volcanic action of the peculiar type we are now considering 

 manifested itself at each of the apices, to a slight extent along the 

 centre of the eastern side, but with much the greatest vigour 

 throughout the northern part of the area. 



II. Petrography. — "We have now to consider the nature of the 

 materials erupted by the volcanic activity of the Puys. As before, 

 it may be convenient to take first the lavas poured out at the 

 surface and the tuffs associated with them, next the products which 

 now fin the orifices of discharge, and lastly the sills, dykes, and 

 veins. 



i. Lavas ejected at the surface, — The geologist who passes from 

 the study of the Plateau lavas to those of the Puys at once remarks 

 the prevalent more basic character of the latter. The great majority 

 of them are basalts, generally oli vine-bearing, and presenting" a 

 number of types. Such more acid rocks as porphyrites occur only 

 rarely. If, however, we select specimens from different centres of 

 eruption we may obtain a range of rock-species from ' ultra-basic 

 materials, such as picrites, to pale porphyrites. 



1. The most basic rock among the bedded basalts is Picrite. 

 Some of the basalts, indeed, approach this rock in poverty of felspar, 

 but I know of only one locality where picrite occurs in such a 

 . ^ The supposed Carboniferous volcanic rocks of Bearhaven on the coast of 

 Cork are noticed on p. 147, note. 



