138 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



this kind are mucli less frequent in the puy- than in the plateau-type. 

 Eut examples may be found in several districts. The most striking 

 v/ith which I am acquainted are those which form so picturesque 

 a group of isolated cones around the volcanic basin of Limerick, 

 especially on the south side. The vents there have been filled by 

 the uprise of much more acid rocks than the lavas of the basin, for, 

 as I have already stated, they include even quartz-porphyry. In 

 the basin of the Firth of Forth some of the prominent bosses of 

 basalt probably mark the sites of former vents, such as Dunearn 

 Hill in Fife, the Castle Eock of Edinburgh, and Galabraes Hill near 

 Eathgate. Some striking vents occur in the Jedburgh district, 

 showing the nearly complete usurpation of the funnel by basalt, but 

 with portions of the tuff still remaining visible. 



In certain examples of puys denudation has not yet proceeded so 

 far as to isolate the column of agglomerate or tuff from the sheets of 

 tuff that were strewn around the old volcano. Hence the actual 

 limits of the vent are still more or less concealed, or at least no 

 sharp line can be drawn between the vent and its ejections. Several 

 admirable illustrations of this relation are to be found in Fife. 

 Thus, in the Saline Hills, seams of coal are actually worked under 

 the surrounding bedded tuffs, the central chimney not having yet 

 been reached. 



2. Bedded Lavas and Tuffs. — In some districts or from certain 

 vents (Midlothian, West Lothian, North Ayrshire, Heads of Ayr) 

 only fine tuff seems to have been thrown out, which we now find 

 intercalated among the surrounding strata. The eruptions of the 

 Puys appear to have been generally neither as vigorous nor as 

 long-continued as those of the Plateaux. They never gave forth 

 such widespread sheets of fragmentary materials as those of Dunbar 

 and the Garlton Hills, or those of the north-east of Ayrshire. A 

 single discharge of ashes seems in many cases to have been the 

 solitary achievement of one of those little volcanoes ; at least only 

 one thin band of tuff may be discoverable to mark its activity. 



When volcanic energy reached its highest intensity during the 

 time of the Puys, not only tuffs, but sheets of lava were emitted, 

 which, gathering round the vent or vents, formed cones or long- 

 connected banks and "ridges. Nowhere in the volcanic history of 

 this country have even the minutest details of that history been 

 so admirably preserved as among the materials erupted from the 

 Carboniferous puys. The volcanoes rose in the shallow lagoons and 

 here and there from deeper parts of the sea-bottom. Their succes- 



